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Experimental Design – Types, Methods, Guide

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Experimental Research Design

Experimental Design

Experimental design is a process of planning and conducting scientific experiments to investigate a hypothesis or research question. It involves carefully designing an experiment that can test the hypothesis, and controlling for other variables that may influence the results.

Experimental design typically includes identifying the variables that will be manipulated or measured, defining the sample or population to be studied, selecting an appropriate method of sampling, choosing a method for data collection and analysis, and determining the appropriate statistical tests to use.

Types of Experimental Design

Here are the different types of experimental design:

Completely Randomized Design

In this design, participants are randomly assigned to one of two or more groups, and each group is exposed to a different treatment or condition.

Randomized Block Design

This design involves dividing participants into blocks based on a specific characteristic, such as age or gender, and then randomly assigning participants within each block to one of two or more treatment groups.

Factorial Design

In a factorial design, participants are randomly assigned to one of several groups, each of which receives a different combination of two or more independent variables.

Repeated Measures Design

In this design, each participant is exposed to all of the different treatments or conditions, either in a random order or in a predetermined order.

Crossover Design

This design involves randomly assigning participants to one of two or more treatment groups, with each group receiving one treatment during the first phase of the study and then switching to a different treatment during the second phase.

Split-plot Design

In this design, the researcher manipulates one or more variables at different levels and uses a randomized block design to control for other variables.

Nested Design

This design involves grouping participants within larger units, such as schools or households, and then randomly assigning these units to different treatment groups.

Laboratory Experiment

Laboratory experiments are conducted under controlled conditions, which allows for greater precision and accuracy. However, because laboratory conditions are not always representative of real-world conditions, the results of these experiments may not be generalizable to the population at large.

Field Experiment

Field experiments are conducted in naturalistic settings and allow for more realistic observations. However, because field experiments are not as controlled as laboratory experiments, they may be subject to more sources of error.

Experimental Design Methods

Experimental design methods refer to the techniques and procedures used to design and conduct experiments in scientific research. Here are some common experimental design methods:

Randomization

This involves randomly assigning participants to different groups or treatments to ensure that any observed differences between groups are due to the treatment and not to other factors.

Control Group

The use of a control group is an important experimental design method that involves having a group of participants that do not receive the treatment or intervention being studied. The control group is used as a baseline to compare the effects of the treatment group.

Blinding involves keeping participants, researchers, or both unaware of which treatment group participants are in, in order to reduce the risk of bias in the results.

Counterbalancing

This involves systematically varying the order in which participants receive treatments or interventions in order to control for order effects.

Replication

Replication involves conducting the same experiment with different samples or under different conditions to increase the reliability and validity of the results.

This experimental design method involves manipulating multiple independent variables simultaneously to investigate their combined effects on the dependent variable.

This involves dividing participants into subgroups or blocks based on specific characteristics, such as age or gender, in order to reduce the risk of confounding variables.

Data Collection Method

Experimental design data collection methods are techniques and procedures used to collect data in experimental research. Here are some common experimental design data collection methods:

Direct Observation

This method involves observing and recording the behavior or phenomenon of interest in real time. It may involve the use of structured or unstructured observation, and may be conducted in a laboratory or naturalistic setting.

Self-report Measures

Self-report measures involve asking participants to report their thoughts, feelings, or behaviors using questionnaires, surveys, or interviews. These measures may be administered in person or online.

Behavioral Measures

Behavioral measures involve measuring participants’ behavior directly, such as through reaction time tasks or performance tests. These measures may be administered using specialized equipment or software.

Physiological Measures

Physiological measures involve measuring participants’ physiological responses, such as heart rate, blood pressure, or brain activity, using specialized equipment. These measures may be invasive or non-invasive, and may be administered in a laboratory or clinical setting.

Archival Data

Archival data involves using existing records or data, such as medical records, administrative records, or historical documents, as a source of information. These data may be collected from public or private sources.

Computerized Measures

Computerized measures involve using software or computer programs to collect data on participants’ behavior or responses. These measures may include reaction time tasks, cognitive tests, or other types of computer-based assessments.

Video Recording

Video recording involves recording participants’ behavior or interactions using cameras or other recording equipment. This method can be used to capture detailed information about participants’ behavior or to analyze social interactions.

Data Analysis Method

Experimental design data analysis methods refer to the statistical techniques and procedures used to analyze data collected in experimental research. Here are some common experimental design data analysis methods:

Descriptive Statistics

Descriptive statistics are used to summarize and describe the data collected in the study. This includes measures such as mean, median, mode, range, and standard deviation.

Inferential Statistics

Inferential statistics are used to make inferences or generalizations about a larger population based on the data collected in the study. This includes hypothesis testing and estimation.

Analysis of Variance (ANOVA)

ANOVA is a statistical technique used to compare means across two or more groups in order to determine whether there are significant differences between the groups. There are several types of ANOVA, including one-way ANOVA, two-way ANOVA, and repeated measures ANOVA.

Regression Analysis

Regression analysis is used to model the relationship between two or more variables in order to determine the strength and direction of the relationship. There are several types of regression analysis, including linear regression, logistic regression, and multiple regression.

Factor Analysis

Factor analysis is used to identify underlying factors or dimensions in a set of variables. This can be used to reduce the complexity of the data and identify patterns in the data.

Structural Equation Modeling (SEM)

SEM is a statistical technique used to model complex relationships between variables. It can be used to test complex theories and models of causality.

Cluster Analysis

Cluster analysis is used to group similar cases or observations together based on similarities or differences in their characteristics.

Time Series Analysis

Time series analysis is used to analyze data collected over time in order to identify trends, patterns, or changes in the data.

Multilevel Modeling

Multilevel modeling is used to analyze data that is nested within multiple levels, such as students nested within schools or employees nested within companies.

Applications of Experimental Design 

Experimental design is a versatile research methodology that can be applied in many fields. Here are some applications of experimental design:

  • Medical Research: Experimental design is commonly used to test new treatments or medications for various medical conditions. This includes clinical trials to evaluate the safety and effectiveness of new drugs or medical devices.
  • Agriculture : Experimental design is used to test new crop varieties, fertilizers, and other agricultural practices. This includes randomized field trials to evaluate the effects of different treatments on crop yield, quality, and pest resistance.
  • Environmental science: Experimental design is used to study the effects of environmental factors, such as pollution or climate change, on ecosystems and wildlife. This includes controlled experiments to study the effects of pollutants on plant growth or animal behavior.
  • Psychology : Experimental design is used to study human behavior and cognitive processes. This includes experiments to test the effects of different interventions, such as therapy or medication, on mental health outcomes.
  • Engineering : Experimental design is used to test new materials, designs, and manufacturing processes in engineering applications. This includes laboratory experiments to test the strength and durability of new materials, or field experiments to test the performance of new technologies.
  • Education : Experimental design is used to evaluate the effectiveness of teaching methods, educational interventions, and programs. This includes randomized controlled trials to compare different teaching methods or evaluate the impact of educational programs on student outcomes.
  • Marketing : Experimental design is used to test the effectiveness of marketing campaigns, pricing strategies, and product designs. This includes experiments to test the impact of different marketing messages or pricing schemes on consumer behavior.

Examples of Experimental Design 

Here are some examples of experimental design in different fields:

  • Example in Medical research : A study that investigates the effectiveness of a new drug treatment for a particular condition. Patients are randomly assigned to either a treatment group or a control group, with the treatment group receiving the new drug and the control group receiving a placebo. The outcomes, such as improvement in symptoms or side effects, are measured and compared between the two groups.
  • Example in Education research: A study that examines the impact of a new teaching method on student learning outcomes. Students are randomly assigned to either a group that receives the new teaching method or a group that receives the traditional teaching method. Student achievement is measured before and after the intervention, and the results are compared between the two groups.
  • Example in Environmental science: A study that tests the effectiveness of a new method for reducing pollution in a river. Two sections of the river are selected, with one section treated with the new method and the other section left untreated. The water quality is measured before and after the intervention, and the results are compared between the two sections.
  • Example in Marketing research: A study that investigates the impact of a new advertising campaign on consumer behavior. Participants are randomly assigned to either a group that is exposed to the new campaign or a group that is not. Their behavior, such as purchasing or product awareness, is measured and compared between the two groups.
  • Example in Social psychology: A study that examines the effect of a new social intervention on reducing prejudice towards a marginalized group. Participants are randomly assigned to either a group that receives the intervention or a control group that does not. Their attitudes and behavior towards the marginalized group are measured before and after the intervention, and the results are compared between the two groups.

When to use Experimental Research Design 

Experimental research design should be used when a researcher wants to establish a cause-and-effect relationship between variables. It is particularly useful when studying the impact of an intervention or treatment on a particular outcome.

Here are some situations where experimental research design may be appropriate:

  • When studying the effects of a new drug or medical treatment: Experimental research design is commonly used in medical research to test the effectiveness and safety of new drugs or medical treatments. By randomly assigning patients to treatment and control groups, researchers can determine whether the treatment is effective in improving health outcomes.
  • When evaluating the effectiveness of an educational intervention: An experimental research design can be used to evaluate the impact of a new teaching method or educational program on student learning outcomes. By randomly assigning students to treatment and control groups, researchers can determine whether the intervention is effective in improving academic performance.
  • When testing the effectiveness of a marketing campaign: An experimental research design can be used to test the effectiveness of different marketing messages or strategies. By randomly assigning participants to treatment and control groups, researchers can determine whether the marketing campaign is effective in changing consumer behavior.
  • When studying the effects of an environmental intervention: Experimental research design can be used to study the impact of environmental interventions, such as pollution reduction programs or conservation efforts. By randomly assigning locations or areas to treatment and control groups, researchers can determine whether the intervention is effective in improving environmental outcomes.
  • When testing the effects of a new technology: An experimental research design can be used to test the effectiveness and safety of new technologies or engineering designs. By randomly assigning participants or locations to treatment and control groups, researchers can determine whether the new technology is effective in achieving its intended purpose.

How to Conduct Experimental Research

Here are the steps to conduct Experimental Research:

  • Identify a Research Question : Start by identifying a research question that you want to answer through the experiment. The question should be clear, specific, and testable.
  • Develop a Hypothesis: Based on your research question, develop a hypothesis that predicts the relationship between the independent and dependent variables. The hypothesis should be clear and testable.
  • Design the Experiment : Determine the type of experimental design you will use, such as a between-subjects design or a within-subjects design. Also, decide on the experimental conditions, such as the number of independent variables, the levels of the independent variable, and the dependent variable to be measured.
  • Select Participants: Select the participants who will take part in the experiment. They should be representative of the population you are interested in studying.
  • Randomly Assign Participants to Groups: If you are using a between-subjects design, randomly assign participants to groups to control for individual differences.
  • Conduct the Experiment : Conduct the experiment by manipulating the independent variable(s) and measuring the dependent variable(s) across the different conditions.
  • Analyze the Data: Analyze the data using appropriate statistical methods to determine if there is a significant effect of the independent variable(s) on the dependent variable(s).
  • Draw Conclusions: Based on the data analysis, draw conclusions about the relationship between the independent and dependent variables. If the results support the hypothesis, then it is accepted. If the results do not support the hypothesis, then it is rejected.
  • Communicate the Results: Finally, communicate the results of the experiment through a research report or presentation. Include the purpose of the study, the methods used, the results obtained, and the conclusions drawn.

Purpose of Experimental Design 

The purpose of experimental design is to control and manipulate one or more independent variables to determine their effect on a dependent variable. Experimental design allows researchers to systematically investigate causal relationships between variables, and to establish cause-and-effect relationships between the independent and dependent variables. Through experimental design, researchers can test hypotheses and make inferences about the population from which the sample was drawn.

Experimental design provides a structured approach to designing and conducting experiments, ensuring that the results are reliable and valid. By carefully controlling for extraneous variables that may affect the outcome of the study, experimental design allows researchers to isolate the effect of the independent variable(s) on the dependent variable(s), and to minimize the influence of other factors that may confound the results.

Experimental design also allows researchers to generalize their findings to the larger population from which the sample was drawn. By randomly selecting participants and using statistical techniques to analyze the data, researchers can make inferences about the larger population with a high degree of confidence.

Overall, the purpose of experimental design is to provide a rigorous, systematic, and scientific method for testing hypotheses and establishing cause-and-effect relationships between variables. Experimental design is a powerful tool for advancing scientific knowledge and informing evidence-based practice in various fields, including psychology, biology, medicine, engineering, and social sciences.

Advantages of Experimental Design 

Experimental design offers several advantages in research. Here are some of the main advantages:

  • Control over extraneous variables: Experimental design allows researchers to control for extraneous variables that may affect the outcome of the study. By manipulating the independent variable and holding all other variables constant, researchers can isolate the effect of the independent variable on the dependent variable.
  • Establishing causality: Experimental design allows researchers to establish causality by manipulating the independent variable and observing its effect on the dependent variable. This allows researchers to determine whether changes in the independent variable cause changes in the dependent variable.
  • Replication : Experimental design allows researchers to replicate their experiments to ensure that the findings are consistent and reliable. Replication is important for establishing the validity and generalizability of the findings.
  • Random assignment: Experimental design often involves randomly assigning participants to conditions. This helps to ensure that individual differences between participants are evenly distributed across conditions, which increases the internal validity of the study.
  • Precision : Experimental design allows researchers to measure variables with precision, which can increase the accuracy and reliability of the data.
  • Generalizability : If the study is well-designed, experimental design can increase the generalizability of the findings. By controlling for extraneous variables and using random assignment, researchers can increase the likelihood that the findings will apply to other populations and contexts.

Limitations of Experimental Design

Experimental design has some limitations that researchers should be aware of. Here are some of the main limitations:

  • Artificiality : Experimental design often involves creating artificial situations that may not reflect real-world situations. This can limit the external validity of the findings, or the extent to which the findings can be generalized to real-world settings.
  • Ethical concerns: Some experimental designs may raise ethical concerns, particularly if they involve manipulating variables that could cause harm to participants or if they involve deception.
  • Participant bias : Participants in experimental studies may modify their behavior in response to the experiment, which can lead to participant bias.
  • Limited generalizability: The conditions of the experiment may not reflect the complexities of real-world situations. As a result, the findings may not be applicable to all populations and contexts.
  • Cost and time : Experimental design can be expensive and time-consuming, particularly if the experiment requires specialized equipment or if the sample size is large.
  • Researcher bias : Researchers may unintentionally bias the results of the experiment if they have expectations or preferences for certain outcomes.
  • Lack of feasibility : Experimental design may not be feasible in some cases, particularly if the research question involves variables that cannot be manipulated or controlled.

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Experimental Design: Types, Examples & Methods

Saul McLeod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

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Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

On This Page:

Experimental design refers to how participants are allocated to different groups in an experiment. Types of design include repeated measures, independent groups, and matched pairs designs.

Probably the most common way to design an experiment in psychology is to divide the participants into two groups, the experimental group and the control group, and then introduce a change to the experimental group, not the control group.

The researcher must decide how he/she will allocate their sample to the different experimental groups.  For example, if there are 10 participants, will all 10 participants participate in both groups (e.g., repeated measures), or will the participants be split in half and take part in only one group each?

Three types of experimental designs are commonly used:

1. Independent Measures

Independent measures design, also known as between-groups , is an experimental design where different participants are used in each condition of the independent variable.  This means that each condition of the experiment includes a different group of participants.

This should be done by random allocation, ensuring that each participant has an equal chance of being assigned to one group.

Independent measures involve using two separate groups of participants, one in each condition. For example:

Independent Measures Design 2

  • Con : More people are needed than with the repeated measures design (i.e., more time-consuming).
  • Pro : Avoids order effects (such as practice or fatigue) as people participate in one condition only.  If a person is involved in several conditions, they may become bored, tired, and fed up by the time they come to the second condition or become wise to the requirements of the experiment!
  • Con : Differences between participants in the groups may affect results, for example, variations in age, gender, or social background.  These differences are known as participant variables (i.e., a type of extraneous variable ).
  • Control : After the participants have been recruited, they should be randomly assigned to their groups. This should ensure the groups are similar, on average (reducing participant variables).

2. Repeated Measures Design

Repeated Measures design is an experimental design where the same participants participate in each independent variable condition.  This means that each experiment condition includes the same group of participants.

Repeated Measures design is also known as within-groups or within-subjects design .

  • Pro : As the same participants are used in each condition, participant variables (i.e., individual differences) are reduced.
  • Con : There may be order effects. Order effects refer to the order of the conditions affecting the participants’ behavior.  Performance in the second condition may be better because the participants know what to do (i.e., practice effect).  Or their performance might be worse in the second condition because they are tired (i.e., fatigue effect). This limitation can be controlled using counterbalancing.
  • Pro : Fewer people are needed as they participate in all conditions (i.e., saves time).
  • Control : To combat order effects, the researcher counter-balances the order of the conditions for the participants.  Alternating the order in which participants perform in different conditions of an experiment.

Counterbalancing

Suppose we used a repeated measures design in which all of the participants first learned words in “loud noise” and then learned them in “no noise.”

We expect the participants to learn better in “no noise” because of order effects, such as practice. However, a researcher can control for order effects using counterbalancing.

The sample would be split into two groups: experimental (A) and control (B).  For example, group 1 does ‘A’ then ‘B,’ and group 2 does ‘B’ then ‘A.’ This is to eliminate order effects.

Although order effects occur for each participant, they balance each other out in the results because they occur equally in both groups.

counter balancing

3. Matched Pairs Design

A matched pairs design is an experimental design where pairs of participants are matched in terms of key variables, such as age or socioeconomic status. One member of each pair is then placed into the experimental group and the other member into the control group .

One member of each matched pair must be randomly assigned to the experimental group and the other to the control group.

matched pairs design

  • Con : If one participant drops out, you lose 2 PPs’ data.
  • Pro : Reduces participant variables because the researcher has tried to pair up the participants so that each condition has people with similar abilities and characteristics.
  • Con : Very time-consuming trying to find closely matched pairs.
  • Pro : It avoids order effects, so counterbalancing is not necessary.
  • Con : Impossible to match people exactly unless they are identical twins!
  • Control : Members of each pair should be randomly assigned to conditions. However, this does not solve all these problems.

Experimental design refers to how participants are allocated to an experiment’s different conditions (or IV levels). There are three types:

1. Independent measures / between-groups : Different participants are used in each condition of the independent variable.

2. Repeated measures /within groups : The same participants take part in each condition of the independent variable.

3. Matched pairs : Each condition uses different participants, but they are matched in terms of important characteristics, e.g., gender, age, intelligence, etc.

Learning Check

Read about each of the experiments below. For each experiment, identify (1) which experimental design was used; and (2) why the researcher might have used that design.

1 . To compare the effectiveness of two different types of therapy for depression, depressed patients were assigned to receive either cognitive therapy or behavior therapy for a 12-week period.

The researchers attempted to ensure that the patients in the two groups had similar severity of depressed symptoms by administering a standardized test of depression to each participant, then pairing them according to the severity of their symptoms.

2 . To assess the difference in reading comprehension between 7 and 9-year-olds, a researcher recruited each group from a local primary school. They were given the same passage of text to read and then asked a series of questions to assess their understanding.

3 . To assess the effectiveness of two different ways of teaching reading, a group of 5-year-olds was recruited from a primary school. Their level of reading ability was assessed, and then they were taught using scheme one for 20 weeks.

At the end of this period, their reading was reassessed, and a reading improvement score was calculated. They were then taught using scheme two for a further 20 weeks, and another reading improvement score for this period was calculated. The reading improvement scores for each child were then compared.

4 . To assess the effect of the organization on recall, a researcher randomly assigned student volunteers to two conditions.

Condition one attempted to recall a list of words that were organized into meaningful categories; condition two attempted to recall the same words, randomly grouped on the page.

Experiment Terminology

Ecological validity.

The degree to which an investigation represents real-life experiences.

Experimenter effects

These are the ways that the experimenter can accidentally influence the participant through their appearance or behavior.

Demand characteristics

The clues in an experiment lead the participants to think they know what the researcher is looking for (e.g., the experimenter’s body language).

Independent variable (IV)

The variable the experimenter manipulates (i.e., changes) is assumed to have a direct effect on the dependent variable.

Dependent variable (DV)

Variable the experimenter measures. This is the outcome (i.e., the result) of a study.

Extraneous variables (EV)

All variables which are not independent variables but could affect the results (DV) of the experiment. Extraneous variables should be controlled where possible.

Confounding variables

Variable(s) that have affected the results (DV), apart from the IV. A confounding variable could be an extraneous variable that has not been controlled.

Random Allocation

Randomly allocating participants to independent variable conditions means that all participants should have an equal chance of taking part in each condition.

The principle of random allocation is to avoid bias in how the experiment is carried out and limit the effects of participant variables.

Order effects

Changes in participants’ performance due to their repeating the same or similar test more than once. Examples of order effects include:

(i) practice effect: an improvement in performance on a task due to repetition, for example, because of familiarity with the task;

(ii) fatigue effect: a decrease in performance of a task due to repetition, for example, because of boredom or tiredness.

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Enago Academy

Experimental Research Design — 6 mistakes you should never make!

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Since school days’ students perform scientific experiments that provide results that define and prove the laws and theorems in science. These experiments are laid on a strong foundation of experimental research designs.

An experimental research design helps researchers execute their research objectives with more clarity and transparency.

In this article, we will not only discuss the key aspects of experimental research designs but also the issues to avoid and problems to resolve while designing your research study.

Table of Contents

What Is Experimental Research Design?

Experimental research design is a framework of protocols and procedures created to conduct experimental research with a scientific approach using two sets of variables. Herein, the first set of variables acts as a constant, used to measure the differences of the second set. The best example of experimental research methods is quantitative research .

Experimental research helps a researcher gather the necessary data for making better research decisions and determining the facts of a research study.

When Can a Researcher Conduct Experimental Research?

A researcher can conduct experimental research in the following situations —

  • When time is an important factor in establishing a relationship between the cause and effect.
  • When there is an invariable or never-changing behavior between the cause and effect.
  • Finally, when the researcher wishes to understand the importance of the cause and effect.

Importance of Experimental Research Design

To publish significant results, choosing a quality research design forms the foundation to build the research study. Moreover, effective research design helps establish quality decision-making procedures, structures the research to lead to easier data analysis, and addresses the main research question. Therefore, it is essential to cater undivided attention and time to create an experimental research design before beginning the practical experiment.

By creating a research design, a researcher is also giving oneself time to organize the research, set up relevant boundaries for the study, and increase the reliability of the results. Through all these efforts, one could also avoid inconclusive results. If any part of the research design is flawed, it will reflect on the quality of the results derived.

Types of Experimental Research Designs

Based on the methods used to collect data in experimental studies, the experimental research designs are of three primary types:

1. Pre-experimental Research Design

A research study could conduct pre-experimental research design when a group or many groups are under observation after implementing factors of cause and effect of the research. The pre-experimental design will help researchers understand whether further investigation is necessary for the groups under observation.

Pre-experimental research is of three types —

  • One-shot Case Study Research Design
  • One-group Pretest-posttest Research Design
  • Static-group Comparison

2. True Experimental Research Design

A true experimental research design relies on statistical analysis to prove or disprove a researcher’s hypothesis. It is one of the most accurate forms of research because it provides specific scientific evidence. Furthermore, out of all the types of experimental designs, only a true experimental design can establish a cause-effect relationship within a group. However, in a true experiment, a researcher must satisfy these three factors —

  • There is a control group that is not subjected to changes and an experimental group that will experience the changed variables
  • A variable that can be manipulated by the researcher
  • Random distribution of the variables

This type of experimental research is commonly observed in the physical sciences.

3. Quasi-experimental Research Design

The word “Quasi” means similarity. A quasi-experimental design is similar to a true experimental design. However, the difference between the two is the assignment of the control group. In this research design, an independent variable is manipulated, but the participants of a group are not randomly assigned. This type of research design is used in field settings where random assignment is either irrelevant or not required.

The classification of the research subjects, conditions, or groups determines the type of research design to be used.

experimental research design

Advantages of Experimental Research

Experimental research allows you to test your idea in a controlled environment before taking the research to clinical trials. Moreover, it provides the best method to test your theory because of the following advantages:

  • Researchers have firm control over variables to obtain results.
  • The subject does not impact the effectiveness of experimental research. Anyone can implement it for research purposes.
  • The results are specific.
  • Post results analysis, research findings from the same dataset can be repurposed for similar research ideas.
  • Researchers can identify the cause and effect of the hypothesis and further analyze this relationship to determine in-depth ideas.
  • Experimental research makes an ideal starting point. The collected data could be used as a foundation to build new research ideas for further studies.

6 Mistakes to Avoid While Designing Your Research

There is no order to this list, and any one of these issues can seriously compromise the quality of your research. You could refer to the list as a checklist of what to avoid while designing your research.

1. Invalid Theoretical Framework

Usually, researchers miss out on checking if their hypothesis is logical to be tested. If your research design does not have basic assumptions or postulates, then it is fundamentally flawed and you need to rework on your research framework.

2. Inadequate Literature Study

Without a comprehensive research literature review , it is difficult to identify and fill the knowledge and information gaps. Furthermore, you need to clearly state how your research will contribute to the research field, either by adding value to the pertinent literature or challenging previous findings and assumptions.

3. Insufficient or Incorrect Statistical Analysis

Statistical results are one of the most trusted scientific evidence. The ultimate goal of a research experiment is to gain valid and sustainable evidence. Therefore, incorrect statistical analysis could affect the quality of any quantitative research.

4. Undefined Research Problem

This is one of the most basic aspects of research design. The research problem statement must be clear and to do that, you must set the framework for the development of research questions that address the core problems.

5. Research Limitations

Every study has some type of limitations . You should anticipate and incorporate those limitations into your conclusion, as well as the basic research design. Include a statement in your manuscript about any perceived limitations, and how you considered them while designing your experiment and drawing the conclusion.

6. Ethical Implications

The most important yet less talked about topic is the ethical issue. Your research design must include ways to minimize any risk for your participants and also address the research problem or question at hand. If you cannot manage the ethical norms along with your research study, your research objectives and validity could be questioned.

Experimental Research Design Example

In an experimental design, a researcher gathers plant samples and then randomly assigns half the samples to photosynthesize in sunlight and the other half to be kept in a dark box without sunlight, while controlling all the other variables (nutrients, water, soil, etc.)

By comparing their outcomes in biochemical tests, the researcher can confirm that the changes in the plants were due to the sunlight and not the other variables.

Experimental research is often the final form of a study conducted in the research process which is considered to provide conclusive and specific results. But it is not meant for every research. It involves a lot of resources, time, and money and is not easy to conduct, unless a foundation of research is built. Yet it is widely used in research institutes and commercial industries, for its most conclusive results in the scientific approach.

Have you worked on research designs? How was your experience creating an experimental design? What difficulties did you face? Do write to us or comment below and share your insights on experimental research designs!

Frequently Asked Questions

Randomization is important in an experimental research because it ensures unbiased results of the experiment. It also measures the cause-effect relationship on a particular group of interest.

Experimental research design lay the foundation of a research and structures the research to establish quality decision making process.

There are 3 types of experimental research designs. These are pre-experimental research design, true experimental research design, and quasi experimental research design.

The difference between an experimental and a quasi-experimental design are: 1. The assignment of the control group in quasi experimental research is non-random, unlike true experimental design, which is randomly assigned. 2. Experimental research group always has a control group; on the other hand, it may not be always present in quasi experimental research.

Experimental research establishes a cause-effect relationship by testing a theory or hypothesis using experimental groups or control variables. In contrast, descriptive research describes a study or a topic by defining the variables under it and answering the questions related to the same.

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  • A Quick Guide to Experimental Design | 5 Steps & Examples

A Quick Guide to Experimental Design | 5 Steps & Examples

Published on 11 April 2022 by Rebecca Bevans . Revised on 5 December 2022.

Experiments are used to study causal relationships . You manipulate one or more independent variables and measure their effect on one or more dependent variables.

Experimental design means creating a set of procedures to systematically test a hypothesis . A good experimental design requires a strong understanding of the system you are studying. 

There are five key steps in designing an experiment:

  • Consider your variables and how they are related
  • Write a specific, testable hypothesis
  • Design experimental treatments to manipulate your independent variable
  • Assign subjects to groups, either between-subjects or within-subjects
  • Plan how you will measure your dependent variable

For valid conclusions, you also need to select a representative sample and control any  extraneous variables that might influence your results. If if random assignment of participants to control and treatment groups is impossible, unethical, or highly difficult, consider an observational study instead.

Table of contents

Step 1: define your variables, step 2: write your hypothesis, step 3: design your experimental treatments, step 4: assign your subjects to treatment groups, step 5: measure your dependent variable, frequently asked questions about experimental design.

You should begin with a specific research question . We will work with two research question examples, one from health sciences and one from ecology:

To translate your research question into an experimental hypothesis, you need to define the main variables and make predictions about how they are related.

Start by simply listing the independent and dependent variables .

Research question Independent variable Dependent variable
Phone use and sleep Minutes of phone use before sleep Hours of sleep per night
Temperature and soil respiration Air temperature just above the soil surface CO2 respired from soil

Then you need to think about possible extraneous and confounding variables and consider how you might control  them in your experiment.

Extraneous variable How to control
Phone use and sleep in sleep patterns among individuals. measure the average difference between sleep with phone use and sleep without phone use rather than the average amount of sleep per treatment group.
Temperature and soil respiration also affects respiration, and moisture can decrease with increasing temperature. monitor soil moisture and add water to make sure that soil moisture is consistent across all treatment plots.

Finally, you can put these variables together into a diagram. Use arrows to show the possible relationships between variables and include signs to show the expected direction of the relationships.

Diagram of the relationship between variables in a sleep experiment

Here we predict that increasing temperature will increase soil respiration and decrease soil moisture, while decreasing soil moisture will lead to decreased soil respiration.

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Now that you have a strong conceptual understanding of the system you are studying, you should be able to write a specific, testable hypothesis that addresses your research question.

Null hypothesis (H ) Alternate hypothesis (H )
Phone use and sleep Phone use before sleep does not correlate with the amount of sleep a person gets. Increasing phone use before sleep leads to a decrease in sleep.
Temperature and soil respiration Air temperature does not correlate with soil respiration. Increased air temperature leads to increased soil respiration.

The next steps will describe how to design a controlled experiment . In a controlled experiment, you must be able to:

  • Systematically and precisely manipulate the independent variable(s).
  • Precisely measure the dependent variable(s).
  • Control any potential confounding variables.

If your study system doesn’t match these criteria, there are other types of research you can use to answer your research question.

How you manipulate the independent variable can affect the experiment’s external validity – that is, the extent to which the results can be generalised and applied to the broader world.

First, you may need to decide how widely to vary your independent variable.

  • just slightly above the natural range for your study region.
  • over a wider range of temperatures to mimic future warming.
  • over an extreme range that is beyond any possible natural variation.

Second, you may need to choose how finely to vary your independent variable. Sometimes this choice is made for you by your experimental system, but often you will need to decide, and this will affect how much you can infer from your results.

  • a categorical variable : either as binary (yes/no) or as levels of a factor (no phone use, low phone use, high phone use).
  • a continuous variable (minutes of phone use measured every night).

How you apply your experimental treatments to your test subjects is crucial for obtaining valid and reliable results.

First, you need to consider the study size : how many individuals will be included in the experiment? In general, the more subjects you include, the greater your experiment’s statistical power , which determines how much confidence you can have in your results.

Then you need to randomly assign your subjects to treatment groups . Each group receives a different level of the treatment (e.g. no phone use, low phone use, high phone use).

You should also include a control group , which receives no treatment. The control group tells us what would have happened to your test subjects without any experimental intervention.

When assigning your subjects to groups, there are two main choices you need to make:

  • A completely randomised design vs a randomised block design .
  • A between-subjects design vs a within-subjects design .

Randomisation

An experiment can be completely randomised or randomised within blocks (aka strata):

  • In a completely randomised design , every subject is assigned to a treatment group at random.
  • In a randomised block design (aka stratified random design), subjects are first grouped according to a characteristic they share, and then randomly assigned to treatments within those groups.
Completely randomised design Randomised block design
Phone use and sleep Subjects are all randomly assigned a level of phone use using a random number generator. Subjects are first grouped by age, and then phone use treatments are randomly assigned within these groups.
Temperature and soil respiration Warming treatments are assigned to soil plots at random by using a number generator to generate map coordinates within the study area. Soils are first grouped by average rainfall, and then treatment plots are randomly assigned within these groups.

Sometimes randomisation isn’t practical or ethical , so researchers create partially-random or even non-random designs. An experimental design where treatments aren’t randomly assigned is called a quasi-experimental design .

Between-subjects vs within-subjects

In a between-subjects design (also known as an independent measures design or classic ANOVA design), individuals receive only one of the possible levels of an experimental treatment.

In medical or social research, you might also use matched pairs within your between-subjects design to make sure that each treatment group contains the same variety of test subjects in the same proportions.

In a within-subjects design (also known as a repeated measures design), every individual receives each of the experimental treatments consecutively, and their responses to each treatment are measured.

Within-subjects or repeated measures can also refer to an experimental design where an effect emerges over time, and individual responses are measured over time in order to measure this effect as it emerges.

Counterbalancing (randomising or reversing the order of treatments among subjects) is often used in within-subjects designs to ensure that the order of treatment application doesn’t influence the results of the experiment.

Between-subjects (independent measures) design Within-subjects (repeated measures) design
Phone use and sleep Subjects are randomly assigned a level of phone use (none, low, or high) and follow that level of phone use throughout the experiment. Subjects are assigned consecutively to zero, low, and high levels of phone use throughout the experiment, and the order in which they follow these treatments is randomised.
Temperature and soil respiration Warming treatments are assigned to soil plots at random and the soils are kept at this temperature throughout the experiment. Every plot receives each warming treatment (1, 3, 5, 8, and 10C above ambient temperatures) consecutively over the course of the experiment, and the order in which they receive these treatments is randomised.

Finally, you need to decide how you’ll collect data on your dependent variable outcomes. You should aim for reliable and valid measurements that minimise bias or error.

Some variables, like temperature, can be objectively measured with scientific instruments. Others may need to be operationalised to turn them into measurable observations.

  • Ask participants to record what time they go to sleep and get up each day.
  • Ask participants to wear a sleep tracker.

How precisely you measure your dependent variable also affects the kinds of statistical analysis you can use on your data.

Experiments are always context-dependent, and a good experimental design will take into account all of the unique considerations of your study system to produce information that is both valid and relevant to your research question.

Experimental designs are a set of procedures that you plan in order to examine the relationship between variables that interest you.

To design a successful experiment, first identify:

  • A testable hypothesis
  • One or more independent variables that you will manipulate
  • One or more dependent variables that you will measure

When designing the experiment, first decide:

  • How your variable(s) will be manipulated
  • How you will control for any potential confounding or lurking variables
  • How many subjects you will include
  • How you will assign treatments to your subjects

The key difference between observational studies and experiments is that, done correctly, an observational study will never influence the responses or behaviours of participants. Experimental designs will have a treatment condition applied to at least a portion of participants.

A confounding variable , also called a confounder or confounding factor, is a third variable in a study examining a potential cause-and-effect relationship.

A confounding variable is related to both the supposed cause and the supposed effect of the study. It can be difficult to separate the true effect of the independent variable from the effect of the confounding variable.

In your research design , it’s important to identify potential confounding variables and plan how you will reduce their impact.

In a between-subjects design , every participant experiences only one condition, and researchers assess group differences between participants in various conditions.

In a within-subjects design , each participant experiences all conditions, and researchers test the same participants repeatedly for differences between conditions.

The word ‘between’ means that you’re comparing different conditions between groups, while the word ‘within’ means you’re comparing different conditions within the same group.

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10 Experimental research

Experimental research—often considered to be the ‘gold standard’ in research designs—is one of the most rigorous of all research designs. In this design, one or more independent variables are manipulated by the researcher (as treatments), subjects are randomly assigned to different treatment levels (random assignment), and the results of the treatments on outcomes (dependent variables) are observed. The unique strength of experimental research is its internal validity (causality) due to its ability to link cause and effect through treatment manipulation, while controlling for the spurious effect of extraneous variable.

Experimental research is best suited for explanatory research—rather than for descriptive or exploratory research—where the goal of the study is to examine cause-effect relationships. It also works well for research that involves a relatively limited and well-defined set of independent variables that can either be manipulated or controlled. Experimental research can be conducted in laboratory or field settings. Laboratory experiments , conducted in laboratory (artificial) settings, tend to be high in internal validity, but this comes at the cost of low external validity (generalisability), because the artificial (laboratory) setting in which the study is conducted may not reflect the real world. Field experiments are conducted in field settings such as in a real organisation, and are high in both internal and external validity. But such experiments are relatively rare, because of the difficulties associated with manipulating treatments and controlling for extraneous effects in a field setting.

Experimental research can be grouped into two broad categories: true experimental designs and quasi-experimental designs. Both designs require treatment manipulation, but while true experiments also require random assignment, quasi-experiments do not. Sometimes, we also refer to non-experimental research, which is not really a research design, but an all-inclusive term that includes all types of research that do not employ treatment manipulation or random assignment, such as survey research, observational research, and correlational studies.

Basic concepts

Treatment and control groups. In experimental research, some subjects are administered one or more experimental stimulus called a treatment (the treatment group ) while other subjects are not given such a stimulus (the control group ). The treatment may be considered successful if subjects in the treatment group rate more favourably on outcome variables than control group subjects. Multiple levels of experimental stimulus may be administered, in which case, there may be more than one treatment group. For example, in order to test the effects of a new drug intended to treat a certain medical condition like dementia, if a sample of dementia patients is randomly divided into three groups, with the first group receiving a high dosage of the drug, the second group receiving a low dosage, and the third group receiving a placebo such as a sugar pill (control group), then the first two groups are experimental groups and the third group is a control group. After administering the drug for a period of time, if the condition of the experimental group subjects improved significantly more than the control group subjects, we can say that the drug is effective. We can also compare the conditions of the high and low dosage experimental groups to determine if the high dose is more effective than the low dose.

Treatment manipulation. Treatments are the unique feature of experimental research that sets this design apart from all other research methods. Treatment manipulation helps control for the ‘cause’ in cause-effect relationships. Naturally, the validity of experimental research depends on how well the treatment was manipulated. Treatment manipulation must be checked using pretests and pilot tests prior to the experimental study. Any measurements conducted before the treatment is administered are called pretest measures , while those conducted after the treatment are posttest measures .

Random selection and assignment. Random selection is the process of randomly drawing a sample from a population or a sampling frame. This approach is typically employed in survey research, and ensures that each unit in the population has a positive chance of being selected into the sample. Random assignment, however, is a process of randomly assigning subjects to experimental or control groups. This is a standard practice in true experimental research to ensure that treatment groups are similar (equivalent) to each other and to the control group prior to treatment administration. Random selection is related to sampling, and is therefore more closely related to the external validity (generalisability) of findings. However, random assignment is related to design, and is therefore most related to internal validity. It is possible to have both random selection and random assignment in well-designed experimental research, but quasi-experimental research involves neither random selection nor random assignment.

Threats to internal validity. Although experimental designs are considered more rigorous than other research methods in terms of the internal validity of their inferences (by virtue of their ability to control causes through treatment manipulation), they are not immune to internal validity threats. Some of these threats to internal validity are described below, within the context of a study of the impact of a special remedial math tutoring program for improving the math abilities of high school students.

History threat is the possibility that the observed effects (dependent variables) are caused by extraneous or historical events rather than by the experimental treatment. For instance, students’ post-remedial math score improvement may have been caused by their preparation for a math exam at their school, rather than the remedial math program.

Maturation threat refers to the possibility that observed effects are caused by natural maturation of subjects (e.g., a general improvement in their intellectual ability to understand complex concepts) rather than the experimental treatment.

Testing threat is a threat in pre-post designs where subjects’ posttest responses are conditioned by their pretest responses. For instance, if students remember their answers from the pretest evaluation, they may tend to repeat them in the posttest exam.

Not conducting a pretest can help avoid this threat.

Instrumentation threat , which also occurs in pre-post designs, refers to the possibility that the difference between pretest and posttest scores is not due to the remedial math program, but due to changes in the administered test, such as the posttest having a higher or lower degree of difficulty than the pretest.

Mortality threat refers to the possibility that subjects may be dropping out of the study at differential rates between the treatment and control groups due to a systematic reason, such that the dropouts were mostly students who scored low on the pretest. If the low-performing students drop out, the results of the posttest will be artificially inflated by the preponderance of high-performing students.

Regression threat —also called a regression to the mean—refers to the statistical tendency of a group’s overall performance to regress toward the mean during a posttest rather than in the anticipated direction. For instance, if subjects scored high on a pretest, they will have a tendency to score lower on the posttest (closer to the mean) because their high scores (away from the mean) during the pretest were possibly a statistical aberration. This problem tends to be more prevalent in non-random samples and when the two measures are imperfectly correlated.

Two-group experimental designs

R

Pretest-posttest control group design . In this design, subjects are randomly assigned to treatment and control groups, subjected to an initial (pretest) measurement of the dependent variables of interest, the treatment group is administered a treatment (representing the independent variable of interest), and the dependent variables measured again (posttest). The notation of this design is shown in Figure 10.1.

Pretest-posttest control group design

Statistical analysis of this design involves a simple analysis of variance (ANOVA) between the treatment and control groups. The pretest-posttest design handles several threats to internal validity, such as maturation, testing, and regression, since these threats can be expected to influence both treatment and control groups in a similar (random) manner. The selection threat is controlled via random assignment. However, additional threats to internal validity may exist. For instance, mortality can be a problem if there are differential dropout rates between the two groups, and the pretest measurement may bias the posttest measurement—especially if the pretest introduces unusual topics or content.

Posttest -only control group design . This design is a simpler version of the pretest-posttest design where pretest measurements are omitted. The design notation is shown in Figure 10.2.

Posttest-only control group design

The treatment effect is measured simply as the difference in the posttest scores between the two groups:

\[E = (O_{1} - O_{2})\,.\]

The appropriate statistical analysis of this design is also a two-group analysis of variance (ANOVA). The simplicity of this design makes it more attractive than the pretest-posttest design in terms of internal validity. This design controls for maturation, testing, regression, selection, and pretest-posttest interaction, though the mortality threat may continue to exist.

C

Because the pretest measure is not a measurement of the dependent variable, but rather a covariate, the treatment effect is measured as the difference in the posttest scores between the treatment and control groups as:

Due to the presence of covariates, the right statistical analysis of this design is a two-group analysis of covariance (ANCOVA). This design has all the advantages of posttest-only design, but with internal validity due to the controlling of covariates. Covariance designs can also be extended to pretest-posttest control group design.

Factorial designs

Two-group designs are inadequate if your research requires manipulation of two or more independent variables (treatments). In such cases, you would need four or higher-group designs. Such designs, quite popular in experimental research, are commonly called factorial designs. Each independent variable in this design is called a factor , and each subdivision of a factor is called a level . Factorial designs enable the researcher to examine not only the individual effect of each treatment on the dependent variables (called main effects), but also their joint effect (called interaction effects).

2 \times 2

In a factorial design, a main effect is said to exist if the dependent variable shows a significant difference between multiple levels of one factor, at all levels of other factors. No change in the dependent variable across factor levels is the null case (baseline), from which main effects are evaluated. In the above example, you may see a main effect of instructional type, instructional time, or both on learning outcomes. An interaction effect exists when the effect of differences in one factor depends upon the level of a second factor. In our example, if the effect of instructional type on learning outcomes is greater for three hours/week of instructional time than for one and a half hours/week, then we can say that there is an interaction effect between instructional type and instructional time on learning outcomes. Note that the presence of interaction effects dominate and make main effects irrelevant, and it is not meaningful to interpret main effects if interaction effects are significant.

Hybrid experimental designs

Hybrid designs are those that are formed by combining features of more established designs. Three such hybrid designs are randomised bocks design, Solomon four-group design, and switched replications design.

Randomised block design. This is a variation of the posttest-only or pretest-posttest control group design where the subject population can be grouped into relatively homogeneous subgroups (called blocks ) within which the experiment is replicated. For instance, if you want to replicate the same posttest-only design among university students and full-time working professionals (two homogeneous blocks), subjects in both blocks are randomly split between the treatment group (receiving the same treatment) and the control group (see Figure 10.5). The purpose of this design is to reduce the ‘noise’ or variance in data that may be attributable to differences between the blocks so that the actual effect of interest can be detected more accurately.

Randomised blocks design

Solomon four-group design . In this design, the sample is divided into two treatment groups and two control groups. One treatment group and one control group receive the pretest, and the other two groups do not. This design represents a combination of posttest-only and pretest-posttest control group design, and is intended to test for the potential biasing effect of pretest measurement on posttest measures that tends to occur in pretest-posttest designs, but not in posttest-only designs. The design notation is shown in Figure 10.6.

Solomon four-group design

Switched replication design . This is a two-group design implemented in two phases with three waves of measurement. The treatment group in the first phase serves as the control group in the second phase, and the control group in the first phase becomes the treatment group in the second phase, as illustrated in Figure 10.7. In other words, the original design is repeated or replicated temporally with treatment/control roles switched between the two groups. By the end of the study, all participants will have received the treatment either during the first or the second phase. This design is most feasible in organisational contexts where organisational programs (e.g., employee training) are implemented in a phased manner or are repeated at regular intervals.

Switched replication design

Quasi-experimental designs

Quasi-experimental designs are almost identical to true experimental designs, but lacking one key ingredient: random assignment. For instance, one entire class section or one organisation is used as the treatment group, while another section of the same class or a different organisation in the same industry is used as the control group. This lack of random assignment potentially results in groups that are non-equivalent, such as one group possessing greater mastery of certain content than the other group, say by virtue of having a better teacher in a previous semester, which introduces the possibility of selection bias . Quasi-experimental designs are therefore inferior to true experimental designs in interval validity due to the presence of a variety of selection related threats such as selection-maturation threat (the treatment and control groups maturing at different rates), selection-history threat (the treatment and control groups being differentially impacted by extraneous or historical events), selection-regression threat (the treatment and control groups regressing toward the mean between pretest and posttest at different rates), selection-instrumentation threat (the treatment and control groups responding differently to the measurement), selection-testing (the treatment and control groups responding differently to the pretest), and selection-mortality (the treatment and control groups demonstrating differential dropout rates). Given these selection threats, it is generally preferable to avoid quasi-experimental designs to the greatest extent possible.

N

In addition, there are quite a few unique non-equivalent designs without corresponding true experimental design cousins. Some of the more useful of these designs are discussed next.

Regression discontinuity (RD) design . This is a non-equivalent pretest-posttest design where subjects are assigned to the treatment or control group based on a cut-off score on a preprogram measure. For instance, patients who are severely ill may be assigned to a treatment group to test the efficacy of a new drug or treatment protocol and those who are mildly ill are assigned to the control group. In another example, students who are lagging behind on standardised test scores may be selected for a remedial curriculum program intended to improve their performance, while those who score high on such tests are not selected from the remedial program.

RD design

Because of the use of a cut-off score, it is possible that the observed results may be a function of the cut-off score rather than the treatment, which introduces a new threat to internal validity. However, using the cut-off score also ensures that limited or costly resources are distributed to people who need them the most, rather than randomly across a population, while simultaneously allowing a quasi-experimental treatment. The control group scores in the RD design do not serve as a benchmark for comparing treatment group scores, given the systematic non-equivalence between the two groups. Rather, if there is no discontinuity between pretest and posttest scores in the control group, but such a discontinuity persists in the treatment group, then this discontinuity is viewed as evidence of the treatment effect.

Proxy pretest design . This design, shown in Figure 10.11, looks very similar to the standard NEGD (pretest-posttest) design, with one critical difference: the pretest score is collected after the treatment is administered. A typical application of this design is when a researcher is brought in to test the efficacy of a program (e.g., an educational program) after the program has already started and pretest data is not available. Under such circumstances, the best option for the researcher is often to use a different prerecorded measure, such as students’ grade point average before the start of the program, as a proxy for pretest data. A variation of the proxy pretest design is to use subjects’ posttest recollection of pretest data, which may be subject to recall bias, but nevertheless may provide a measure of perceived gain or change in the dependent variable.

Proxy pretest design

Separate pretest-posttest samples design . This design is useful if it is not possible to collect pretest and posttest data from the same subjects for some reason. As shown in Figure 10.12, there are four groups in this design, but two groups come from a single non-equivalent group, while the other two groups come from a different non-equivalent group. For instance, say you want to test customer satisfaction with a new online service that is implemented in one city but not in another. In this case, customers in the first city serve as the treatment group and those in the second city constitute the control group. If it is not possible to obtain pretest and posttest measures from the same customers, you can measure customer satisfaction at one point in time, implement the new service program, and measure customer satisfaction (with a different set of customers) after the program is implemented. Customer satisfaction is also measured in the control group at the same times as in the treatment group, but without the new program implementation. The design is not particularly strong, because you cannot examine the changes in any specific customer’s satisfaction score before and after the implementation, but you can only examine average customer satisfaction scores. Despite the lower internal validity, this design may still be a useful way of collecting quasi-experimental data when pretest and posttest data is not available from the same subjects.

Separate pretest-posttest samples design

An interesting variation of the NEDV design is a pattern-matching NEDV design , which employs multiple outcome variables and a theory that explains how much each variable will be affected by the treatment. The researcher can then examine if the theoretical prediction is matched in actual observations. This pattern-matching technique—based on the degree of correspondence between theoretical and observed patterns—is a powerful way of alleviating internal validity concerns in the original NEDV design.

NEDV design

Perils of experimental research

Experimental research is one of the most difficult of research designs, and should not be taken lightly. This type of research is often best with a multitude of methodological problems. First, though experimental research requires theories for framing hypotheses for testing, much of current experimental research is atheoretical. Without theories, the hypotheses being tested tend to be ad hoc, possibly illogical, and meaningless. Second, many of the measurement instruments used in experimental research are not tested for reliability and validity, and are incomparable across studies. Consequently, results generated using such instruments are also incomparable. Third, often experimental research uses inappropriate research designs, such as irrelevant dependent variables, no interaction effects, no experimental controls, and non-equivalent stimulus across treatment groups. Findings from such studies tend to lack internal validity and are highly suspect. Fourth, the treatments (tasks) used in experimental research may be diverse, incomparable, and inconsistent across studies, and sometimes inappropriate for the subject population. For instance, undergraduate student subjects are often asked to pretend that they are marketing managers and asked to perform a complex budget allocation task in which they have no experience or expertise. The use of such inappropriate tasks, introduces new threats to internal validity (i.e., subject’s performance may be an artefact of the content or difficulty of the task setting), generates findings that are non-interpretable and meaningless, and makes integration of findings across studies impossible.

The design of proper experimental treatments is a very important task in experimental design, because the treatment is the raison d’etre of the experimental method, and must never be rushed or neglected. To design an adequate and appropriate task, researchers should use prevalidated tasks if available, conduct treatment manipulation checks to check for the adequacy of such tasks (by debriefing subjects after performing the assigned task), conduct pilot tests (repeatedly, if necessary), and if in doubt, use tasks that are simple and familiar for the respondent sample rather than tasks that are complex or unfamiliar.

In summary, this chapter introduced key concepts in the experimental design research method and introduced a variety of true experimental and quasi-experimental designs. Although these designs vary widely in internal validity, designs with less internal validity should not be overlooked and may sometimes be useful under specific circumstances and empirical contingencies.

Social Science Research: Principles, Methods and Practices (Revised edition) Copyright © 2019 by Anol Bhattacherjee is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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  • Experimental Research Designs: Types, Examples & Methods

busayo.longe

Experimental research is the most familiar type of research design for individuals in the physical sciences and a host of other fields. This is mainly because experimental research is a classical scientific experiment, similar to those performed in high school science classes.

Imagine taking 2 samples of the same plant and exposing one of them to sunlight, while the other is kept away from sunlight. Let the plant exposed to sunlight be called sample A, while the latter is called sample B.

If after the duration of the research, we find out that sample A grows and sample B dies, even though they are both regularly wetted and given the same treatment. Therefore, we can conclude that sunlight will aid growth in all similar plants.

What is Experimental Research?

Experimental research is a scientific approach to research, where one or more independent variables are manipulated and applied to one or more dependent variables to measure their effect on the latter. The effect of the independent variables on the dependent variables is usually observed and recorded over some time, to aid researchers in drawing a reasonable conclusion regarding the relationship between these 2 variable types.

The experimental research method is widely used in physical and social sciences, psychology, and education. It is based on the comparison between two or more groups with a straightforward logic, which may, however, be difficult to execute.

Mostly related to a laboratory test procedure, experimental research designs involve collecting quantitative data and performing statistical analysis on them during research. Therefore, making it an example of quantitative research method .

What are The Types of Experimental Research Design?

The types of experimental research design are determined by the way the researcher assigns subjects to different conditions and groups. They are of 3 types, namely; pre-experimental, quasi-experimental, and true experimental research.

Pre-experimental Research Design

In pre-experimental research design, either a group or various dependent groups are observed for the effect of the application of an independent variable which is presumed to cause change. It is the simplest form of experimental research design and is treated with no control group.

Although very practical, experimental research is lacking in several areas of the true-experimental criteria. The pre-experimental research design is further divided into three types

  • One-shot Case Study Research Design

In this type of experimental study, only one dependent group or variable is considered. The study is carried out after some treatment which was presumed to cause change, making it a posttest study.

  • One-group Pretest-posttest Research Design: 

This research design combines both posttest and pretest study by carrying out a test on a single group before the treatment is administered and after the treatment is administered. With the former being administered at the beginning of treatment and later at the end.

  • Static-group Comparison: 

In a static-group comparison study, 2 or more groups are placed under observation, where only one of the groups is subjected to some treatment while the other groups are held static. All the groups are post-tested, and the observed differences between the groups are assumed to be a result of the treatment.

Quasi-experimental Research Design

  The word “quasi” means partial, half, or pseudo. Therefore, the quasi-experimental research bearing a resemblance to the true experimental research, but not the same.  In quasi-experiments, the participants are not randomly assigned, and as such, they are used in settings where randomization is difficult or impossible.

 This is very common in educational research, where administrators are unwilling to allow the random selection of students for experimental samples.

Some examples of quasi-experimental research design include; the time series, no equivalent control group design, and the counterbalanced design.

True Experimental Research Design

The true experimental research design relies on statistical analysis to approve or disprove a hypothesis. It is the most accurate type of experimental design and may be carried out with or without a pretest on at least 2 randomly assigned dependent subjects.

The true experimental research design must contain a control group, a variable that can be manipulated by the researcher, and the distribution must be random. The classification of true experimental design include:

  • The posttest-only Control Group Design: In this design, subjects are randomly selected and assigned to the 2 groups (control and experimental), and only the experimental group is treated. After close observation, both groups are post-tested, and a conclusion is drawn from the difference between these groups.
  • The pretest-posttest Control Group Design: For this control group design, subjects are randomly assigned to the 2 groups, both are presented, but only the experimental group is treated. After close observation, both groups are post-tested to measure the degree of change in each group.
  • Solomon four-group Design: This is the combination of the pretest-only and the pretest-posttest control groups. In this case, the randomly selected subjects are placed into 4 groups.

The first two of these groups are tested using the posttest-only method, while the other two are tested using the pretest-posttest method.

Examples of Experimental Research

Experimental research examples are different, depending on the type of experimental research design that is being considered. The most basic example of experimental research is laboratory experiments, which may differ in nature depending on the subject of research.

Administering Exams After The End of Semester

During the semester, students in a class are lectured on particular courses and an exam is administered at the end of the semester. In this case, the students are the subjects or dependent variables while the lectures are the independent variables treated on the subjects.

Only one group of carefully selected subjects are considered in this research, making it a pre-experimental research design example. We will also notice that tests are only carried out at the end of the semester, and not at the beginning.

Further making it easy for us to conclude that it is a one-shot case study research. 

Employee Skill Evaluation

Before employing a job seeker, organizations conduct tests that are used to screen out less qualified candidates from the pool of qualified applicants. This way, organizations can determine an employee’s skill set at the point of employment.

In the course of employment, organizations also carry out employee training to improve employee productivity and generally grow the organization. Further evaluation is carried out at the end of each training to test the impact of the training on employee skills, and test for improvement.

Here, the subject is the employee, while the treatment is the training conducted. This is a pretest-posttest control group experimental research example.

Evaluation of Teaching Method

Let us consider an academic institution that wants to evaluate the teaching method of 2 teachers to determine which is best. Imagine a case whereby the students assigned to each teacher is carefully selected probably due to personal request by parents or due to stubbornness and smartness.

This is a no equivalent group design example because the samples are not equal. By evaluating the effectiveness of each teacher’s teaching method this way, we may conclude after a post-test has been carried out.

However, this may be influenced by factors like the natural sweetness of a student. For example, a very smart student will grab more easily than his or her peers irrespective of the method of teaching.

What are the Characteristics of Experimental Research?  

Experimental research contains dependent, independent and extraneous variables. The dependent variables are the variables being treated or manipulated and are sometimes called the subject of the research.

The independent variables are the experimental treatment being exerted on the dependent variables. Extraneous variables, on the other hand, are other factors affecting the experiment that may also contribute to the change.

The setting is where the experiment is carried out. Many experiments are carried out in the laboratory, where control can be exerted on the extraneous variables, thereby eliminating them.

Other experiments are carried out in a less controllable setting. The choice of setting used in research depends on the nature of the experiment being carried out.

  • Multivariable

Experimental research may include multiple independent variables, e.g. time, skills, test scores, etc.

Why Use Experimental Research Design?  

Experimental research design can be majorly used in physical sciences, social sciences, education, and psychology. It is used to make predictions and draw conclusions on a subject matter. 

Some uses of experimental research design are highlighted below.

  • Medicine: Experimental research is used to provide the proper treatment for diseases. In most cases, rather than directly using patients as the research subject, researchers take a sample of the bacteria from the patient’s body and are treated with the developed antibacterial

The changes observed during this period are recorded and evaluated to determine its effectiveness. This process can be carried out using different experimental research methods.

  • Education: Asides from science subjects like Chemistry and Physics which involves teaching students how to perform experimental research, it can also be used in improving the standard of an academic institution. This includes testing students’ knowledge on different topics, coming up with better teaching methods, and the implementation of other programs that will aid student learning.
  • Human Behavior: Social scientists are the ones who mostly use experimental research to test human behaviour. For example, consider 2 people randomly chosen to be the subject of the social interaction research where one person is placed in a room without human interaction for 1 year.

The other person is placed in a room with a few other people, enjoying human interaction. There will be a difference in their behaviour at the end of the experiment.

  • UI/UX: During the product development phase, one of the major aims of the product team is to create a great user experience with the product. Therefore, before launching the final product design, potential are brought in to interact with the product.

For example, when finding it difficult to choose how to position a button or feature on the app interface, a random sample of product testers are allowed to test the 2 samples and how the button positioning influences the user interaction is recorded.

What are the Disadvantages of Experimental Research?  

  • It is highly prone to human error due to its dependency on variable control which may not be properly implemented. These errors could eliminate the validity of the experiment and the research being conducted.
  • Exerting control of extraneous variables may create unrealistic situations. Eliminating real-life variables will result in inaccurate conclusions. This may also result in researchers controlling the variables to suit his or her personal preferences.
  • It is a time-consuming process. So much time is spent on testing dependent variables and waiting for the effect of the manipulation of dependent variables to manifest.
  • It is expensive.
  • It is very risky and may have ethical complications that cannot be ignored. This is common in medical research, where failed trials may lead to a patient’s death or a deteriorating health condition.
  • Experimental research results are not descriptive.
  • Response bias can also be supplied by the subject of the conversation.
  • Human responses in experimental research can be difficult to measure.

What are the Data Collection Methods in Experimental Research?  

Data collection methods in experimental research are the different ways in which data can be collected for experimental research. They are used in different cases, depending on the type of research being carried out.

1. Observational Study

This type of study is carried out over a long period. It measures and observes the variables of interest without changing existing conditions.

When researching the effect of social interaction on human behavior, the subjects who are placed in 2 different environments are observed throughout the research. No matter the kind of absurd behavior that is exhibited by the subject during this period, its condition will not be changed.

This may be a very risky thing to do in medical cases because it may lead to death or worse medical conditions.

2. Simulations

This procedure uses mathematical, physical, or computer models to replicate a real-life process or situation. It is frequently used when the actual situation is too expensive, dangerous, or impractical to replicate in real life.

This method is commonly used in engineering and operational research for learning purposes and sometimes as a tool to estimate possible outcomes of real research. Some common situation software are Simulink, MATLAB, and Simul8.

Not all kinds of experimental research can be carried out using simulation as a data collection tool . It is very impractical for a lot of laboratory-based research that involves chemical processes.

A survey is a tool used to gather relevant data about the characteristics of a population and is one of the most common data collection tools. A survey consists of a group of questions prepared by the researcher, to be answered by the research subject.

Surveys can be shared with the respondents both physically and electronically. When collecting data through surveys, the kind of data collected depends on the respondent, and researchers have limited control over it.

Formplus is the best tool for collecting experimental data using survey s. It has relevant features that will aid the data collection process and can also be used in other aspects of experimental research.

Differences between Experimental and Non-Experimental Research 

1. In experimental research, the researcher can control and manipulate the environment of the research, including the predictor variable which can be changed. On the other hand, non-experimental research cannot be controlled or manipulated by the researcher at will.

This is because it takes place in a real-life setting, where extraneous variables cannot be eliminated. Therefore, it is more difficult to conclude non-experimental studies, even though they are much more flexible and allow for a greater range of study fields.

2. The relationship between cause and effect cannot be established in non-experimental research, while it can be established in experimental research. This may be because many extraneous variables also influence the changes in the research subject, making it difficult to point at a particular variable as the cause of a particular change

3. Independent variables are not introduced, withdrawn, or manipulated in non-experimental designs, but the same may not be said about experimental research.

Experimental Research vs. Alternatives and When to Use Them

1. experimental research vs causal comparative.

Experimental research enables you to control variables and identify how the independent variable affects the dependent variable. Causal-comparative find out the cause-and-effect relationship between the variables by comparing already existing groups that are affected differently by the independent variable.

For example, in an experiment to see how K-12 education affects children and teenager development. An experimental research would split the children into groups, some would get formal K-12 education, while others won’t. This is not ethically right because every child has the right to education. So, what we do instead would be to compare already existing groups of children who are getting formal education with those who due to some circumstances can not.

Pros and Cons of Experimental vs Causal-Comparative Research

  • Causal-Comparative:   Strengths:  More realistic than experiments, can be conducted in real-world settings.  Weaknesses:  Establishing causality can be weaker due to the lack of manipulation.

2. Experimental Research vs Correlational Research

When experimenting, you are trying to establish a cause-and-effect relationship between different variables. For example, you are trying to establish the effect of heat on water, the temperature keeps changing (independent variable) and you see how it affects the water (dependent variable).

For correlational research, you are not necessarily interested in the why or the cause-and-effect relationship between the variables, you are focusing on the relationship. Using the same water and temperature example, you are only interested in the fact that they change, you are not investigating which of the variables or other variables causes them to change.

Pros and Cons of Experimental vs Correlational Research

3. experimental research vs descriptive research.

With experimental research, you alter the independent variable to see how it affects the dependent variable, but with descriptive research you are simply studying the characteristics of the variable you are studying.

So, in an experiment to see how blown glass reacts to temperature, experimental research would keep altering the temperature to varying levels of high and low to see how it affects the dependent variable (glass). But descriptive research would investigate the glass properties.

Pros and Cons of Experimental vs Descriptive Research

4. experimental research vs action research.

Experimental research tests for causal relationships by focusing on one independent variable vs the dependent variable and keeps other variables constant. So, you are testing hypotheses and using the information from the research to contribute to knowledge.

However, with action research, you are using a real-world setting which means you are not controlling variables. You are also performing the research to solve actual problems and improve already established practices.

For example, if you are testing for how long commutes affect workers’ productivity. With experimental research, you would vary the length of commute to see how the time affects work. But with action research, you would account for other factors such as weather, commute route, nutrition, etc. Also, experimental research helps know the relationship between commute time and productivity, while action research helps you look for ways to improve productivity

Pros and Cons of Experimental vs Action Research

Conclusion  .

Experimental research designs are often considered to be the standard in research designs. This is partly due to the common misconception that research is equivalent to scientific experiments—a component of experimental research design.

In this research design, one or more subjects or dependent variables are randomly assigned to different treatments (i.e. independent variables manipulated by the researcher) and the results are observed to conclude. One of the uniqueness of experimental research is in its ability to control the effect of extraneous variables.

Experimental research is suitable for research whose goal is to examine cause-effect relationships, e.g. explanatory research. It can be conducted in the laboratory or field settings, depending on the aim of the research that is being carried out. 

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Experimental design: Guide, steps, examples

Last updated

27 April 2023

Reviewed by

Miroslav Damyanov

Short on time? Get an AI generated summary of this article instead

Experimental research design is a scientific framework that allows you to manipulate one or more variables while controlling the test environment. 

When testing a theory or new product, it can be helpful to have a certain level of control and manipulate variables to discover different outcomes. You can use these experiments to determine cause and effect or study variable associations. 

This guide explores the types of experimental design, the steps in designing an experiment, and the advantages and limitations of experimental design. 

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  • What is experimental research design?

You can determine the relationship between each of the variables by: 

Manipulating one or more independent variables (i.e., stimuli or treatments)

Applying the changes to one or more dependent variables (i.e., test groups or outcomes)

With the ability to analyze the relationship between variables and using measurable data, you can increase the accuracy of the result. 

What is a good experimental design?

A good experimental design requires: 

Significant planning to ensure control over the testing environment

Sound experimental treatments

Properly assigning subjects to treatment groups

Without proper planning, unexpected external variables can alter an experiment's outcome. 

To meet your research goals, your experimental design should include these characteristics:

Provide unbiased estimates of inputs and associated uncertainties

Enable the researcher to detect differences caused by independent variables

Include a plan for analysis and reporting of the results

Provide easily interpretable results with specific conclusions

What's the difference between experimental and quasi-experimental design?

The major difference between experimental and quasi-experimental design is the random assignment of subjects to groups. 

A true experiment relies on certain controls. Typically, the researcher designs the treatment and randomly assigns subjects to control and treatment groups. 

However, these conditions are unethical or impossible to achieve in some situations.

When it's unethical or impractical to assign participants randomly, that’s when a quasi-experimental design comes in. 

This design allows researchers to conduct a similar experiment by assigning subjects to groups based on non-random criteria. 

Another type of quasi-experimental design might occur when the researcher doesn't have control over the treatment but studies pre-existing groups after they receive different treatments.

When can a researcher conduct experimental research?

Various settings and professions can use experimental research to gather information and observe behavior in controlled settings. 

Basically, a researcher can conduct experimental research any time they want to test a theory with variable and dependent controls. 

Experimental research is an option when the project includes an independent variable and a desire to understand the relationship between cause and effect. 

  • The importance of experimental research design

Experimental research enables researchers to conduct studies that provide specific, definitive answers to questions and hypotheses. 

Researchers can test Independent variables in controlled settings to:

Test the effectiveness of a new medication

Design better products for consumers

Answer questions about human health and behavior

Developing a quality research plan means a researcher can accurately answer vital research questions with minimal error. As a result, definitive conclusions can influence the future of the independent variable. 

Types of experimental research designs

There are three main types of experimental research design. The research type you use will depend on the criteria of your experiment, your research budget, and environmental limitations. 

Pre-experimental research design

A pre-experimental research study is a basic observational study that monitors independent variables’ effects. 

During research, you observe one or more groups after applying a treatment to test whether the treatment causes any change. 

The three subtypes of pre-experimental research design are:

One-shot case study research design

This research method introduces a single test group to a single stimulus to study the results at the end of the application. 

After researchers presume the stimulus or treatment has caused changes, they gather results to determine how it affects the test subjects. 

One-group pretest-posttest design

This method uses a single test group but includes a pretest study as a benchmark. The researcher applies a test before and after the group’s exposure to a specific stimulus. 

Static group comparison design

This method includes two or more groups, enabling the researcher to use one group as a control. They apply a stimulus to one group and leave the other group static. 

A posttest study compares the results among groups. 

True experimental research design

A true experiment is the most common research method. It involves statistical analysis to prove or disprove a specific hypothesis . 

Under completely experimental conditions, researchers expose participants in two or more randomized groups to different stimuli. 

Random selection removes any potential for bias, providing more reliable results. 

These are the three main sub-groups of true experimental research design:

Posttest-only control group design

This structure requires the researcher to divide participants into two random groups. One group receives no stimuli and acts as a control while the other group experiences stimuli.

Researchers perform a test at the end of the experiment to observe the stimuli exposure results.

Pretest-posttest control group design

This test also requires two groups. It includes a pretest as a benchmark before introducing the stimulus. 

The pretest introduces multiple ways to test subjects. For instance, if the control group also experiences a change, it reveals that taking the test twice changes the results.

Solomon four-group design

This structure divides subjects into two groups, with two as control groups. Researchers assign the first control group a posttest only and the second control group a pretest and a posttest. 

The two variable groups mirror the control groups, but researchers expose them to stimuli. The ability to differentiate between groups in multiple ways provides researchers with more testing approaches for data-based conclusions. 

Quasi-experimental research design

Although closely related to a true experiment, quasi-experimental research design differs in approach and scope. 

Quasi-experimental research design doesn’t have randomly selected participants. Researchers typically divide the groups in this research by pre-existing differences. 

Quasi-experimental research is more common in educational studies, nursing, or other research projects where it's not ethical or practical to use randomized subject groups.

  • 5 steps for designing an experiment

Experimental research requires a clearly defined plan to outline the research parameters and expected goals. 

Here are five key steps in designing a successful experiment:

Step 1: Define variables and their relationship

Your experiment should begin with a question: What are you hoping to learn through your experiment? 

The relationship between variables in your study will determine your answer.

Define the independent variable (the intended stimuli) and the dependent variable (the expected effect of the stimuli). After identifying these groups, consider how you might control them in your experiment. 

Could natural variations affect your research? If so, your experiment should include a pretest and posttest. 

Step 2: Develop a specific, testable hypothesis

With a firm understanding of the system you intend to study, you can write a specific, testable hypothesis. 

What is the expected outcome of your study? 

Develop a prediction about how the independent variable will affect the dependent variable. 

How will the stimuli in your experiment affect your test subjects? 

Your hypothesis should provide a prediction of the answer to your research question . 

Step 3: Design experimental treatments to manipulate your independent variable

Depending on your experiment, your variable may be a fixed stimulus (like a medical treatment) or a variable stimulus (like a period during which an activity occurs). 

Determine which type of stimulus meets your experiment’s needs and how widely or finely to vary your stimuli. 

Step 4: Assign subjects to groups

When you have a clear idea of how to carry out your experiment, you can determine how to assemble test groups for an accurate study. 

When choosing your study groups, consider: 

The size of your experiment

Whether you can select groups randomly

Your target audience for the outcome of the study

You should be able to create groups with an equal number of subjects and include subjects that match your target audience. Remember, you should assign one group as a control and use one or more groups to study the effects of variables. 

Step 5: Plan how to measure your dependent variable

This step determines how you'll collect data to determine the study's outcome. You should seek reliable and valid measurements that minimize research bias or error. 

You can measure some data with scientific tools, while you’ll need to operationalize other forms to turn them into measurable observations.

  • Advantages of experimental research

Experimental research is an integral part of our world. It allows researchers to conduct experiments that answer specific questions. 

While researchers use many methods to conduct different experiments, experimental research offers these distinct benefits:

Researchers can determine cause and effect by manipulating variables.

It gives researchers a high level of control.

Researchers can test multiple variables within a single experiment.

All industries and fields of knowledge can use it. 

Researchers can duplicate results to promote the validity of the study .

Replicating natural settings rapidly means immediate research.

Researchers can combine it with other research methods.

It provides specific conclusions about the validity of a product, theory, or idea.

  • Disadvantages (or limitations) of experimental research

Unfortunately, no research type yields ideal conditions or perfect results. 

While experimental research might be the right choice for some studies, certain conditions could render experiments useless or even dangerous. 

Before conducting experimental research, consider these disadvantages and limitations:

Required professional qualification

Only competent professionals with an academic degree and specific training are qualified to conduct rigorous experimental research. This ensures results are unbiased and valid. 

Limited scope

Experimental research may not capture the complexity of some phenomena, such as social interactions or cultural norms. These are difficult to control in a laboratory setting.

Resource-intensive

Experimental research can be expensive, time-consuming, and require significant resources, such as specialized equipment or trained personnel.

Limited generalizability

The controlled nature means the research findings may not fully apply to real-world situations or people outside the experimental setting.

Practical or ethical concerns

Some experiments may involve manipulating variables that could harm participants or violate ethical guidelines . 

Researchers must ensure their experiments do not cause harm or discomfort to participants. 

Sometimes, recruiting a sample of people to randomly assign may be difficult. 

  • Experimental research design example

Experiments across all industries and research realms provide scientists, developers, and other researchers with definitive answers. These experiments can solve problems, create inventions, and heal illnesses. 

Product design testing is an excellent example of experimental research. 

A company in the product development phase creates multiple prototypes for testing. With a randomized selection, researchers introduce each test group to a different prototype. 

When groups experience different product designs , the company can assess which option most appeals to potential customers. 

Experimental research design provides researchers with a controlled environment to conduct experiments that evaluate cause and effect. 

Using the five steps to develop a research plan ensures you anticipate and eliminate external variables while answering life’s crucial questions.

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experimental design research methodology

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Experimental Research: What it is + Types of designs

Experimental Research Design

Any research conducted under scientifically acceptable conditions uses experimental methods. The success of experimental studies hinges on researchers confirming the change of a variable is based solely on the manipulation of the constant variable. The research should establish a notable cause and effect.

What is Experimental Research?

Experimental research is a study conducted with a scientific approach using two sets of variables. The first set acts as a constant, which you use to measure the differences of the second set. Quantitative research methods , for example, are experimental.

If you don’t have enough data to support your decisions, you must first determine the facts. This research gathers the data necessary to help you make better decisions.

You can conduct experimental research in the following situations:

  • Time is a vital factor in establishing a relationship between cause and effect.
  • Invariable behavior between cause and effect.
  • You wish to understand the importance of cause and effect.

Experimental Research Design Types

The classic experimental design definition is: “The methods used to collect data in experimental studies.”

There are three primary types of experimental design:

  • Pre-experimental research design
  • True experimental research design
  • Quasi-experimental research design

The way you classify research subjects based on conditions or groups determines the type of research design  you should use.

0 1. Pre-Experimental Design

A group, or various groups, are kept under observation after implementing cause and effect factors. You’ll conduct this research to understand whether further investigation is necessary for these particular groups.

You can break down pre-experimental research further into three types:

  • One-shot Case Study Research Design
  • One-group Pretest-posttest Research Design
  • Static-group Comparison

0 2. True Experimental Design

It relies on statistical analysis to prove or disprove a hypothesis, making it the most accurate form of research. Of the types of experimental design, only true design can establish a cause-effect relationship within a group. In a true experiment, three factors need to be satisfied:

  • There is a Control Group, which won’t be subject to changes, and an Experimental Group, which will experience the changed variables.
  • A variable that can be manipulated by the researcher
  • Random distribution

This experimental research method commonly occurs in the physical sciences.

0 3. Quasi-Experimental Design

The word “Quasi” indicates similarity. A quasi-experimental design is similar to an experimental one, but it is not the same. The difference between the two is the assignment of a control group. In this research, an independent variable is manipulated, but the participants of a group are not randomly assigned. Quasi-research is used in field settings where random assignment is either irrelevant or not required.

Importance of Experimental Design

Experimental research is a powerful tool for understanding cause-and-effect relationships. It allows us to manipulate variables and observe the effects, which is crucial for understanding how different factors influence the outcome of a study.

But the importance of experimental research goes beyond that. It’s a critical method for many scientific and academic studies. It allows us to test theories, develop new products, and make groundbreaking discoveries.

For example, this research is essential for developing new drugs and medical treatments. Researchers can understand how a new drug works by manipulating dosage and administration variables and identifying potential side effects.

Similarly, experimental research is used in the field of psychology to test theories and understand human behavior. By manipulating variables such as stimuli, researchers can gain insights into how the brain works and identify new treatment options for mental health disorders.

It is also widely used in the field of education. It allows educators to test new teaching methods and identify what works best. By manipulating variables such as class size, teaching style, and curriculum, researchers can understand how students learn and identify new ways to improve educational outcomes.

In addition, experimental research is a powerful tool for businesses and organizations. By manipulating variables such as marketing strategies, product design, and customer service, companies can understand what works best and identify new opportunities for growth.

Advantages of Experimental Research

When talking about this research, we can think of human life. Babies do their own rudimentary experiments (such as putting objects in their mouths) to learn about the world around them, while older children and teens do experiments at school to learn more about science.

Ancient scientists used this research to prove that their hypotheses were correct. For example, Galileo Galilei and Antoine Lavoisier conducted various experiments to discover key concepts in physics and chemistry. The same is true of modern experts, who use this scientific method to see if new drugs are effective, discover treatments for diseases, and create new electronic devices (among others).

It’s vital to test new ideas or theories. Why put time, effort, and funding into something that may not work?

This research allows you to test your idea in a controlled environment before marketing. It also provides the best method to test your theory thanks to the following advantages:

Advantages of experimental research

  • Researchers have a stronger hold over variables to obtain desired results.
  • The subject or industry does not impact the effectiveness of experimental research. Any industry can implement it for research purposes.
  • The results are specific.
  • After analyzing the results, you can apply your findings to similar ideas or situations.
  • You can identify the cause and effect of a hypothesis. Researchers can further analyze this relationship to determine more in-depth ideas.
  • Experimental research makes an ideal starting point. The data you collect is a foundation for building more ideas and conducting more action research .

Whether you want to know how the public will react to a new product or if a certain food increases the chance of disease, experimental research is the best place to start. Begin your research by finding subjects using  QuestionPro Audience  and other tools today.

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Statistics By Jim

Making statistics intuitive

Experimental Design: Definition and Types

By Jim Frost 3 Comments

What is Experimental Design?

An experimental design is a detailed plan for collecting and using data to identify causal relationships. Through careful planning, the design of experiments allows your data collection efforts to have a reasonable chance of detecting effects and testing hypotheses that answer your research questions.

An experiment is a data collection procedure that occurs in controlled conditions to identify and understand causal relationships between variables. Researchers can use many potential designs. The ultimate choice depends on their research question, resources, goals, and constraints. In some fields of study, researchers refer to experimental design as the design of experiments (DOE). Both terms are synonymous.

Scientist who developed an experimental design for her research.

Ultimately, the design of experiments helps ensure that your procedures and data will evaluate your research question effectively. Without an experimental design, you might waste your efforts in a process that, for many potential reasons, can’t answer your research question. In short, it helps you trust your results.

Learn more about Independent and Dependent Variables .

Design of Experiments: Goals & Settings

Experiments occur in many settings, ranging from psychology, social sciences, medicine, physics, engineering, and industrial and service sectors. Typically, experimental goals are to discover a previously unknown effect , confirm a known effect, or test a hypothesis.

Effects represent causal relationships between variables. For example, in a medical experiment, does the new medicine cause an improvement in health outcomes? If so, the medicine has a causal effect on the outcome.

An experimental design’s focus depends on the subject area and can include the following goals:

  • Understanding the relationships between variables.
  • Identifying the variables that have the largest impact on the outcomes.
  • Finding the input variable settings that produce an optimal result.

For example, psychologists have conducted experiments to understand how conformity affects decision-making. Sociologists have performed experiments to determine whether ethnicity affects the public reaction to staged bike thefts. These experiments map out the causal relationships between variables, and their primary goal is to understand the role of various factors.

Conversely, in a manufacturing environment, the researchers might use an experimental design to find the factors that most effectively improve their product’s strength, identify the optimal manufacturing settings, and do all that while accounting for various constraints. In short, a manufacturer’s goal is often to use experiments to improve their products cost-effectively.

In a medical experiment, the goal might be to quantify the medicine’s effect and find the optimum dosage.

Developing an Experimental Design

Developing an experimental design involves planning that maximizes the potential to collect data that is both trustworthy and able to detect causal relationships. Specifically, these studies aim to see effects when they exist in the population the researchers are studying, preferentially favor causal effects, isolate each factor’s true effect from potential confounders, and produce conclusions that you can generalize to the real world.

To accomplish these goals, experimental designs carefully manage data validity and reliability , and internal and external experimental validity. When your experiment is valid and reliable, you can expect your procedures and data to produce trustworthy results.

An excellent experimental design involves the following:

  • Lots of preplanning.
  • Developing experimental treatments.
  • Determining how to assign subjects to treatment groups.

The remainder of this article focuses on how experimental designs incorporate these essential items to accomplish their research goals.

Learn more about Data Reliability vs. Validity and Internal and External Experimental Validity .

Preplanning, Defining, and Operationalizing for Design of Experiments

A literature review is crucial for the design of experiments.

This phase of the design of experiments helps you identify critical variables, know how to measure them while ensuring reliability and validity, and understand the relationships between them. The review can also help you find ways to reduce sources of variability, which increases your ability to detect treatment effects. Notably, the literature review allows you to learn how similar studies designed their experiments and the challenges they faced.

Operationalizing a study involves taking your research question, using the background information you gathered, and formulating an actionable plan.

This process should produce a specific and testable hypothesis using data that you can reasonably collect given the resources available to the experiment.

  • Null hypothesis : The jumping exercise intervention does not affect bone density.
  • Alternative hypothesis : The jumping exercise intervention affects bone density.

To learn more about this early phase, read Five Steps for Conducting Scientific Studies with Statistical Analyses .

Formulating Treatments in Experimental Designs

In an experimental design, treatments are variables that the researchers control. They are the primary independent variables of interest. Researchers administer the treatment to the subjects or items in the experiment and want to know whether it causes changes in the outcome.

As the name implies, a treatment can be medical in nature, such as a new medicine or vaccine. But it’s a general term that applies to other things such as training programs, manufacturing settings, teaching methods, and types of fertilizers. I helped run an experiment where the treatment was a jumping exercise intervention that we hoped would increase bone density. All these treatment examples are things that potentially influence a measurable outcome.

Even when you know your treatment generally, you must carefully consider the amount. How large of a dose? If you’re comparing three different temperatures in a manufacturing process, how far apart are they? For my bone mineral density study, we had to determine how frequently the exercise sessions would occur and how long each lasted.

How you define the treatments in the design of experiments can affect your findings and the generalizability of your results.

Assigning Subjects to Experimental Groups

A crucial decision for all experimental designs is determining how researchers assign subjects to the experimental conditions—the treatment and control groups. The control group is often, but not always, the lack of a treatment. It serves as a basis for comparison by showing outcomes for subjects who don’t receive a treatment. Learn more about Control Groups .

How your experimental design assigns subjects to the groups affects how confident you can be that the findings represent true causal effects rather than mere correlation caused by confounders. Indeed, the assignment method influences how you control for confounding variables. This is the difference between correlation and causation .

Imagine a study finds that vitamin consumption correlates with better health outcomes. As a researcher, you want to be able to say that vitamin consumption causes the improvements. However, with the wrong experimental design, you might only be able to say there is an association. A confounder, and not the vitamins, might actually cause the health benefits.

Let’s explore some of the ways to assign subjects in design of experiments.

Completely Randomized Designs

A completely randomized experimental design randomly assigns all subjects to the treatment and control groups. You simply take each participant and use a random process to determine their group assignment. You can flip coins, roll a die, or use a computer. Randomized experiments must be prospective studies because they need to be able to control group assignment.

Random assignment in the design of experiments helps ensure that the groups are roughly equivalent at the beginning of the study. This equivalence at the start increases your confidence that any differences you see at the end were caused by the treatments. The randomization tends to equalize confounders between the experimental groups and, thereby, cancels out their effects, leaving only the treatment effects.

For example, in a vitamin study, the researchers can randomly assign participants to either the control or vitamin group. Because the groups are approximately equal when the experiment starts, if the health outcomes are different at the end of the study, the researchers can be confident that the vitamins caused those improvements.

Statisticians consider randomized experimental designs to be the best for identifying causal relationships.

If you can’t randomly assign subjects but want to draw causal conclusions about an intervention, consider using a quasi-experimental design .

Learn more about Randomized Controlled Trials and Random Assignment in Experiments .

Randomized Block Designs

Nuisance factors are variables that can affect the outcome, but they are not the researcher’s primary interest. Unfortunately, they can hide or distort the treatment results. When experimenters know about specific nuisance factors, they can use a randomized block design to minimize their impact.

This experimental design takes subjects with a shared “nuisance” characteristic and groups them into blocks. The participants in each block are then randomly assigned to the experimental groups. This process allows the experiment to control for known nuisance factors.

Blocking in the design of experiments reduces the impact of nuisance factors on experimental error. The analysis assesses the effects of the treatment within each block, which removes the variability between blocks. The result is that blocked experimental designs can reduce the impact of nuisance variables, increasing the ability to detect treatment effects accurately.

Suppose you’re testing various teaching methods. Because grade level likely affects educational outcomes, you might use grade level as a blocking factor. To use a randomized block design for this scenario, divide the participants by grade level and then randomly assign the members of each grade level to the experimental groups.

A standard guideline for an experimental design is to “Block what you can, randomize what you cannot.” Use blocking for a few primary nuisance factors. Then use random assignment to distribute the unblocked nuisance factors equally between the experimental conditions.

You can also use covariates to control nuisance factors. Learn about Covariates: Definition and Uses .

Observational Studies

In some experimental designs, randomly assigning subjects to the experimental conditions is impossible or unethical. The researchers simply can’t assign participants to the experimental groups. However, they can observe them in their natural groupings, measure the essential variables, and look for correlations. These observational studies are also known as quasi-experimental designs. Retrospective studies must be observational in nature because they look back at past events.

Imagine you’re studying the effects of depression on an activity. Clearly, you can’t randomly assign participants to the depression and control groups. But you can observe participants with and without depression and see how their task performance differs.

Observational studies let you perform research when you can’t control the treatment. However, quasi-experimental designs increase the problem of confounding variables. For this design of experiments, correlation does not necessarily imply causation. While special procedures can help control confounders in an observational study, you’re ultimately less confident that the results represent causal findings.

Learn more about Observational Studies .

For a good comparison, learn about the differences and tradeoffs between Observational Studies and Randomized Experiments .

Between-Subjects vs. Within-Subjects Experimental Designs

When you think of the design of experiments, you probably picture a treatment and control group. Researchers assign participants to only one of these groups, so each group contains entirely different subjects than the other groups. Analysts compare the groups at the end of the experiment. Statisticians refer to this method as a between-subjects, or independent measures, experimental design.

In a between-subjects design , you can have more than one treatment group, but each subject is exposed to only one condition, the control group or one of the treatment groups.

A potential downside to this approach is that differences between groups at the beginning can affect the results at the end. As you’ve read earlier, random assignment can reduce those differences, but it is imperfect. There will always be some variability between the groups.

In a  within-subjects experimental design , also known as repeated measures, subjects experience all treatment conditions and are measured for each. Each subject acts as their own control, which reduces variability and increases the statistical power to detect effects.

In this experimental design, you minimize pre-existing differences between the experimental conditions because they all contain the same subjects. However, the order of treatments can affect the results. Beware of practice and fatigue effects. Learn more about Repeated Measures Designs .

Assigned to one experimental condition Participates in all experimental conditions
Requires more subjects Fewer subjects
Differences between subjects in the groups can affect the results Uses same subjects in all conditions.
No order of treatment effects. Order of treatments can affect results.

Design of Experiments Examples

For example, a bone density study has three experimental groups—a control group, a stretching exercise group, and a jumping exercise group.

In a between-subjects experimental design, scientists randomly assign each participant to one of the three groups.

In a within-subjects design, all subjects experience the three conditions sequentially while the researchers measure bone density repeatedly. The procedure can switch the order of treatments for the participants to help reduce order effects.

Matched Pairs Experimental Design

A matched pairs experimental design is a between-subjects study that uses pairs of similar subjects. Researchers use this approach to reduce pre-existing differences between experimental groups. It’s yet another design of experiments method for reducing sources of variability.

Researchers identify variables likely to affect the outcome, such as demographics. When they pick a subject with a set of characteristics, they try to locate another participant with similar attributes to create a matched pair. Scientists randomly assign one member of a pair to the treatment group and the other to the control group.

On the plus side, this process creates two similar groups, and it doesn’t create treatment order effects. While matched pairs do not produce the perfectly matched groups of a within-subjects design (which uses the same subjects in all conditions), it aims to reduce variability between groups relative to a between-subjects study.

On the downside, finding matched pairs is very time-consuming. Additionally, if one member of a matched pair drops out, the other subject must leave the study too.

Learn more about Matched Pairs Design: Uses & Examples .

Another consideration is whether you’ll use a cross-sectional design (one point in time) or use a longitudinal study to track changes over time .

A case study is a research method that often serves as a precursor to a more rigorous experimental design by identifying research questions, variables, and hypotheses to test. Learn more about What is a Case Study? Definition & Examples .

In conclusion, the design of experiments is extremely sensitive to subject area concerns and the time and resources available to the researchers. Developing a suitable experimental design requires balancing a multitude of considerations. A successful design is necessary to obtain trustworthy answers to your research question and to have a reasonable chance of detecting treatment effects when they exist.

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  • Types of Research Designs Compared | Guide & Examples

Types of Research Designs Compared | Guide & Examples

Published on June 20, 2019 by Shona McCombes . Revised on June 22, 2023.

When you start planning a research project, developing research questions and creating a  research design , you will have to make various decisions about the type of research you want to do.

There are many ways to categorize different types of research. The words you use to describe your research depend on your discipline and field. In general, though, the form your research design takes will be shaped by:

  • The type of knowledge you aim to produce
  • The type of data you will collect and analyze
  • The sampling methods , timescale and location of the research

This article takes a look at some common distinctions made between different types of research and outlines the key differences between them.

Table of contents

Types of research aims, types of research data, types of sampling, timescale, and location, other interesting articles.

The first thing to consider is what kind of knowledge your research aims to contribute.

Type of research What’s the difference? What to consider
Basic vs. applied Basic research aims to , while applied research aims to . Do you want to expand scientific understanding or solve a practical problem?
vs. Exploratory research aims to , while explanatory research aims to . How much is already known about your research problem? Are you conducting initial research on a newly-identified issue, or seeking precise conclusions about an established issue?
aims to , while aims to . Is there already some theory on your research problem that you can use to develop , or do you want to propose new theories based on your findings?

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The next thing to consider is what type of data you will collect. Each kind of data is associated with a range of specific research methods and procedures.

Type of research What’s the difference? What to consider
Primary research vs secondary research Primary data is (e.g., through or ), while secondary data (e.g., in government or scientific publications). How much data is already available on your topic? Do you want to collect original data or analyze existing data (e.g., through a )?
, while . Is your research more concerned with measuring something or interpreting something? You can also create a research design that has elements of both.
vs Descriptive research gathers data , while experimental research . Do you want to identify characteristics, patterns and or test causal relationships between ?

Finally, you have to consider three closely related questions: how will you select the subjects or participants of the research? When and how often will you collect data from your subjects? And where will the research take place?

Keep in mind that the methods that you choose bring with them different risk factors and types of research bias . Biases aren’t completely avoidable, but can heavily impact the validity and reliability of your findings if left unchecked.

Type of research What’s the difference? What to consider
allows you to , while allows you to draw conclusions . Do you want to produce  knowledge that applies to many contexts or detailed knowledge about a specific context (e.g. in a )?
vs Cross-sectional studies , while longitudinal studies . Is your research question focused on understanding the current situation or tracking changes over time?
Field research vs laboratory research Field research takes place in , while laboratory research takes place in . Do you want to find out how something occurs in the real world or draw firm conclusions about cause and effect? Laboratory experiments have higher but lower .
Fixed design vs flexible design In a fixed research design the subjects, timescale and location are begins, while in a flexible design these aspects may . Do you want to test hypotheses and establish generalizable facts, or explore concepts and develop understanding? For measuring, testing and making generalizations, a fixed research design has higher .

Choosing between all these different research types is part of the process of creating your research design , which determines exactly how your research will be conducted. But the type of research is only the first step: next, you have to make more concrete decisions about your research methods and the details of the study.

Read more about creating a research design

If you want to know more about statistics , methodology , or research bias , make sure to check out some of our other articles with explanations and examples.

  • Normal distribution
  • Degrees of freedom
  • Null hypothesis
  • Discourse analysis
  • Control groups
  • Mixed methods research
  • Non-probability sampling
  • Quantitative research
  • Ecological validity

Research bias

  • Rosenthal effect
  • Implicit bias
  • Cognitive bias
  • Selection bias
  • Negativity bias
  • Status quo bias

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19+ Experimental Design Examples (Methods + Types)

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Ever wondered how scientists discover new medicines, psychologists learn about behavior, or even how marketers figure out what kind of ads you like? Well, they all have something in common: they use a special plan or recipe called an "experimental design."

Imagine you're baking cookies. You can't just throw random amounts of flour, sugar, and chocolate chips into a bowl and hope for the best. You follow a recipe, right? Scientists and researchers do something similar. They follow a "recipe" called an experimental design to make sure their experiments are set up in a way that the answers they find are meaningful and reliable.

Experimental design is the roadmap researchers use to answer questions. It's a set of rules and steps that researchers follow to collect information, or "data," in a way that is fair, accurate, and makes sense.

experimental design test tubes

Long ago, people didn't have detailed game plans for experiments. They often just tried things out and saw what happened. But over time, people got smarter about this. They started creating structured plans—what we now call experimental designs—to get clearer, more trustworthy answers to their questions.

In this article, we'll take you on a journey through the world of experimental designs. We'll talk about the different types, or "flavors," of experimental designs, where they're used, and even give you a peek into how they came to be.

What Is Experimental Design?

Alright, before we dive into the different types of experimental designs, let's get crystal clear on what experimental design actually is.

Imagine you're a detective trying to solve a mystery. You need clues, right? Well, in the world of research, experimental design is like the roadmap that helps you find those clues. It's like the game plan in sports or the blueprint when you're building a house. Just like you wouldn't start building without a good blueprint, researchers won't start their studies without a strong experimental design.

So, why do we need experimental design? Think about baking a cake. If you toss ingredients into a bowl without measuring, you'll end up with a mess instead of a tasty dessert.

Similarly, in research, if you don't have a solid plan, you might get confusing or incorrect results. A good experimental design helps you ask the right questions ( think critically ), decide what to measure ( come up with an idea ), and figure out how to measure it (test it). It also helps you consider things that might mess up your results, like outside influences you hadn't thought of.

For example, let's say you want to find out if listening to music helps people focus better. Your experimental design would help you decide things like: Who are you going to test? What kind of music will you use? How will you measure focus? And, importantly, how will you make sure that it's really the music affecting focus and not something else, like the time of day or whether someone had a good breakfast?

In short, experimental design is the master plan that guides researchers through the process of collecting data, so they can answer questions in the most reliable way possible. It's like the GPS for the journey of discovery!

History of Experimental Design

Around 350 BCE, people like Aristotle were trying to figure out how the world works, but they mostly just thought really hard about things. They didn't test their ideas much. So while they were super smart, their methods weren't always the best for finding out the truth.

Fast forward to the Renaissance (14th to 17th centuries), a time of big changes and lots of curiosity. People like Galileo started to experiment by actually doing tests, like rolling balls down inclined planes to study motion. Galileo's work was cool because he combined thinking with doing. He'd have an idea, test it, look at the results, and then think some more. This approach was a lot more reliable than just sitting around and thinking.

Now, let's zoom ahead to the 18th and 19th centuries. This is when people like Francis Galton, an English polymath, started to get really systematic about experimentation. Galton was obsessed with measuring things. Seriously, he even tried to measure how good-looking people were ! His work helped create the foundations for a more organized approach to experiments.

Next stop: the early 20th century. Enter Ronald A. Fisher , a brilliant British statistician. Fisher was a game-changer. He came up with ideas that are like the bread and butter of modern experimental design.

Fisher invented the concept of the " control group "—that's a group of people or things that don't get the treatment you're testing, so you can compare them to those who do. He also stressed the importance of " randomization ," which means assigning people or things to different groups by chance, like drawing names out of a hat. This makes sure the experiment is fair and the results are trustworthy.

Around the same time, American psychologists like John B. Watson and B.F. Skinner were developing " behaviorism ." They focused on studying things that they could directly observe and measure, like actions and reactions.

Skinner even built boxes—called Skinner Boxes —to test how animals like pigeons and rats learn. Their work helped shape how psychologists design experiments today. Watson performed a very controversial experiment called The Little Albert experiment that helped describe behaviour through conditioning—in other words, how people learn to behave the way they do.

In the later part of the 20th century and into our time, computers have totally shaken things up. Researchers now use super powerful software to help design their experiments and crunch the numbers.

With computers, they can simulate complex experiments before they even start, which helps them predict what might happen. This is especially helpful in fields like medicine, where getting things right can be a matter of life and death.

Also, did you know that experimental designs aren't just for scientists in labs? They're used by people in all sorts of jobs, like marketing, education, and even video game design! Yes, someone probably ran an experiment to figure out what makes a game super fun to play.

So there you have it—a quick tour through the history of experimental design, from Aristotle's deep thoughts to Fisher's groundbreaking ideas, and all the way to today's computer-powered research. These designs are the recipes that help people from all walks of life find answers to their big questions.

Key Terms in Experimental Design

Before we dig into the different types of experimental designs, let's get comfy with some key terms. Understanding these terms will make it easier for us to explore the various types of experimental designs that researchers use to answer their big questions.

Independent Variable : This is what you change or control in your experiment to see what effect it has. Think of it as the "cause" in a cause-and-effect relationship. For example, if you're studying whether different types of music help people focus, the kind of music is the independent variable.

Dependent Variable : This is what you're measuring to see the effect of your independent variable. In our music and focus experiment, how well people focus is the dependent variable—it's what "depends" on the kind of music played.

Control Group : This is a group of people who don't get the special treatment or change you're testing. They help you see what happens when the independent variable is not applied. If you're testing whether a new medicine works, the control group would take a fake pill, called a placebo , instead of the real medicine.

Experimental Group : This is the group that gets the special treatment or change you're interested in. Going back to our medicine example, this group would get the actual medicine to see if it has any effect.

Randomization : This is like shaking things up in a fair way. You randomly put people into the control or experimental group so that each group is a good mix of different kinds of people. This helps make the results more reliable.

Sample : This is the group of people you're studying. They're a "sample" of a larger group that you're interested in. For instance, if you want to know how teenagers feel about a new video game, you might study a sample of 100 teenagers.

Bias : This is anything that might tilt your experiment one way or another without you realizing it. Like if you're testing a new kind of dog food and you only test it on poodles, that could create a bias because maybe poodles just really like that food and other breeds don't.

Data : This is the information you collect during the experiment. It's like the treasure you find on your journey of discovery!

Replication : This means doing the experiment more than once to make sure your findings hold up. It's like double-checking your answers on a test.

Hypothesis : This is your educated guess about what will happen in the experiment. It's like predicting the end of a movie based on the first half.

Steps of Experimental Design

Alright, let's say you're all fired up and ready to run your own experiment. Cool! But where do you start? Well, designing an experiment is a bit like planning a road trip. There are some key steps you've got to take to make sure you reach your destination. Let's break it down:

  • Ask a Question : Before you hit the road, you've got to know where you're going. Same with experiments. You start with a question you want to answer, like "Does eating breakfast really make you do better in school?"
  • Do Some Homework : Before you pack your bags, you look up the best places to visit, right? In science, this means reading up on what other people have already discovered about your topic.
  • Form a Hypothesis : This is your educated guess about what you think will happen. It's like saying, "I bet this route will get us there faster."
  • Plan the Details : Now you decide what kind of car you're driving (your experimental design), who's coming with you (your sample), and what snacks to bring (your variables).
  • Randomization : Remember, this is like shuffling a deck of cards. You want to mix up who goes into your control and experimental groups to make sure it's a fair test.
  • Run the Experiment : Finally, the rubber hits the road! You carry out your plan, making sure to collect your data carefully.
  • Analyze the Data : Once the trip's over, you look at your photos and decide which ones are keepers. In science, this means looking at your data to see what it tells you.
  • Draw Conclusions : Based on your data, did you find an answer to your question? This is like saying, "Yep, that route was faster," or "Nope, we hit a ton of traffic."
  • Share Your Findings : After a great trip, you want to tell everyone about it, right? Scientists do the same by publishing their results so others can learn from them.
  • Do It Again? : Sometimes one road trip just isn't enough. In the same way, scientists often repeat their experiments to make sure their findings are solid.

So there you have it! Those are the basic steps you need to follow when you're designing an experiment. Each step helps make sure that you're setting up a fair and reliable way to find answers to your big questions.

Let's get into examples of experimental designs.

1) True Experimental Design

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In the world of experiments, the True Experimental Design is like the superstar quarterback everyone talks about. Born out of the early 20th-century work of statisticians like Ronald A. Fisher, this design is all about control, precision, and reliability.

Researchers carefully pick an independent variable to manipulate (remember, that's the thing they're changing on purpose) and measure the dependent variable (the effect they're studying). Then comes the magic trick—randomization. By randomly putting participants into either the control or experimental group, scientists make sure their experiment is as fair as possible.

No sneaky biases here!

True Experimental Design Pros

The pros of True Experimental Design are like the perks of a VIP ticket at a concert: you get the best and most trustworthy results. Because everything is controlled and randomized, you can feel pretty confident that the results aren't just a fluke.

True Experimental Design Cons

However, there's a catch. Sometimes, it's really tough to set up these experiments in a real-world situation. Imagine trying to control every single detail of your day, from the food you eat to the air you breathe. Not so easy, right?

True Experimental Design Uses

The fields that get the most out of True Experimental Designs are those that need super reliable results, like medical research.

When scientists were developing COVID-19 vaccines, they used this design to run clinical trials. They had control groups that received a placebo (a harmless substance with no effect) and experimental groups that got the actual vaccine. Then they measured how many people in each group got sick. By comparing the two, they could say, "Yep, this vaccine works!"

So next time you read about a groundbreaking discovery in medicine or technology, chances are a True Experimental Design was the VIP behind the scenes, making sure everything was on point. It's been the go-to for rigorous scientific inquiry for nearly a century, and it's not stepping off the stage anytime soon.

2) Quasi-Experimental Design

So, let's talk about the Quasi-Experimental Design. Think of this one as the cool cousin of True Experimental Design. It wants to be just like its famous relative, but it's a bit more laid-back and flexible. You'll find quasi-experimental designs when it's tricky to set up a full-blown True Experimental Design with all the bells and whistles.

Quasi-experiments still play with an independent variable, just like their stricter cousins. The big difference? They don't use randomization. It's like wanting to divide a bag of jelly beans equally between your friends, but you can't quite do it perfectly.

In real life, it's often not possible or ethical to randomly assign people to different groups, especially when dealing with sensitive topics like education or social issues. And that's where quasi-experiments come in.

Quasi-Experimental Design Pros

Even though they lack full randomization, quasi-experimental designs are like the Swiss Army knives of research: versatile and practical. They're especially popular in fields like education, sociology, and public policy.

For instance, when researchers wanted to figure out if the Head Start program , aimed at giving young kids a "head start" in school, was effective, they used a quasi-experimental design. They couldn't randomly assign kids to go or not go to preschool, but they could compare kids who did with kids who didn't.

Quasi-Experimental Design Cons

Of course, quasi-experiments come with their own bag of pros and cons. On the plus side, they're easier to set up and often cheaper than true experiments. But the flip side is that they're not as rock-solid in their conclusions. Because the groups aren't randomly assigned, there's always that little voice saying, "Hey, are we missing something here?"

Quasi-Experimental Design Uses

Quasi-Experimental Design gained traction in the mid-20th century. Researchers were grappling with real-world problems that didn't fit neatly into a laboratory setting. Plus, as society became more aware of ethical considerations, the need for flexible designs increased. So, the quasi-experimental approach was like a breath of fresh air for scientists wanting to study complex issues without a laundry list of restrictions.

In short, if True Experimental Design is the superstar quarterback, Quasi-Experimental Design is the versatile player who can adapt and still make significant contributions to the game.

3) Pre-Experimental Design

Now, let's talk about the Pre-Experimental Design. Imagine it as the beginner's skateboard you get before you try out for all the cool tricks. It has wheels, it rolls, but it's not built for the professional skatepark.

Similarly, pre-experimental designs give researchers a starting point. They let you dip your toes in the water of scientific research without diving in head-first.

So, what's the deal with pre-experimental designs?

Pre-Experimental Designs are the basic, no-frills versions of experiments. Researchers still mess around with an independent variable and measure a dependent variable, but they skip over the whole randomization thing and often don't even have a control group.

It's like baking a cake but forgetting the frosting and sprinkles; you'll get some results, but they might not be as complete or reliable as you'd like.

Pre-Experimental Design Pros

Why use such a simple setup? Because sometimes, you just need to get the ball rolling. Pre-experimental designs are great for quick-and-dirty research when you're short on time or resources. They give you a rough idea of what's happening, which you can use to plan more detailed studies later.

A good example of this is early studies on the effects of screen time on kids. Researchers couldn't control every aspect of a child's life, but they could easily ask parents to track how much time their kids spent in front of screens and then look for trends in behavior or school performance.

Pre-Experimental Design Cons

But here's the catch: pre-experimental designs are like that first draft of an essay. It helps you get your ideas down, but you wouldn't want to turn it in for a grade. Because these designs lack the rigorous structure of true or quasi-experimental setups, they can't give you rock-solid conclusions. They're more like clues or signposts pointing you in a certain direction.

Pre-Experimental Design Uses

This type of design became popular in the early stages of various scientific fields. Researchers used them to scratch the surface of a topic, generate some initial data, and then decide if it's worth exploring further. In other words, pre-experimental designs were the stepping stones that led to more complex, thorough investigations.

So, while Pre-Experimental Design may not be the star player on the team, it's like the practice squad that helps everyone get better. It's the starting point that can lead to bigger and better things.

4) Factorial Design

Now, buckle up, because we're moving into the world of Factorial Design, the multi-tasker of the experimental universe.

Imagine juggling not just one, but multiple balls in the air—that's what researchers do in a factorial design.

In Factorial Design, researchers are not satisfied with just studying one independent variable. Nope, they want to study two or more at the same time to see how they interact.

It's like cooking with several spices to see how they blend together to create unique flavors.

Factorial Design became the talk of the town with the rise of computers. Why? Because this design produces a lot of data, and computers are the number crunchers that help make sense of it all. So, thanks to our silicon friends, researchers can study complicated questions like, "How do diet AND exercise together affect weight loss?" instead of looking at just one of those factors.

Factorial Design Pros

This design's main selling point is its ability to explore interactions between variables. For instance, maybe a new study drug works really well for young people but not so great for older adults. A factorial design could reveal that age is a crucial factor, something you might miss if you only studied the drug's effectiveness in general. It's like being a detective who looks for clues not just in one room but throughout the entire house.

Factorial Design Cons

However, factorial designs have their own bag of challenges. First off, they can be pretty complicated to set up and run. Imagine coordinating a four-way intersection with lots of cars coming from all directions—you've got to make sure everything runs smoothly, or you'll end up with a traffic jam. Similarly, researchers need to carefully plan how they'll measure and analyze all the different variables.

Factorial Design Uses

Factorial designs are widely used in psychology to untangle the web of factors that influence human behavior. They're also popular in fields like marketing, where companies want to understand how different aspects like price, packaging, and advertising influence a product's success.

And speaking of success, the factorial design has been a hit since statisticians like Ronald A. Fisher (yep, him again!) expanded on it in the early-to-mid 20th century. It offered a more nuanced way of understanding the world, proving that sometimes, to get the full picture, you've got to juggle more than one ball at a time.

So, if True Experimental Design is the quarterback and Quasi-Experimental Design is the versatile player, Factorial Design is the strategist who sees the entire game board and makes moves accordingly.

5) Longitudinal Design

pill bottle

Alright, let's take a step into the world of Longitudinal Design. Picture it as the grand storyteller, the kind who doesn't just tell you about a single event but spins an epic tale that stretches over years or even decades. This design isn't about quick snapshots; it's about capturing the whole movie of someone's life or a long-running process.

You know how you might take a photo every year on your birthday to see how you've changed? Longitudinal Design is kind of like that, but for scientific research.

With Longitudinal Design, instead of measuring something just once, researchers come back again and again, sometimes over many years, to see how things are going. This helps them understand not just what's happening, but why it's happening and how it changes over time.

This design really started to shine in the latter half of the 20th century, when researchers began to realize that some questions can't be answered in a hurry. Think about studies that look at how kids grow up, or research on how a certain medicine affects you over a long period. These aren't things you can rush.

The famous Framingham Heart Study , started in 1948, is a prime example. It's been studying heart health in a small town in Massachusetts for decades, and the findings have shaped what we know about heart disease.

Longitudinal Design Pros

So, what's to love about Longitudinal Design? First off, it's the go-to for studying change over time, whether that's how people age or how a forest recovers from a fire.

Longitudinal Design Cons

But it's not all sunshine and rainbows. Longitudinal studies take a lot of patience and resources. Plus, keeping track of participants over many years can be like herding cats—difficult and full of surprises.

Longitudinal Design Uses

Despite these challenges, longitudinal studies have been key in fields like psychology, sociology, and medicine. They provide the kind of deep, long-term insights that other designs just can't match.

So, if the True Experimental Design is the superstar quarterback, and the Quasi-Experimental Design is the flexible athlete, then the Factorial Design is the strategist, and the Longitudinal Design is the wise elder who has seen it all and has stories to tell.

6) Cross-Sectional Design

Now, let's flip the script and talk about Cross-Sectional Design, the polar opposite of the Longitudinal Design. If Longitudinal is the grand storyteller, think of Cross-Sectional as the snapshot photographer. It captures a single moment in time, like a selfie that you take to remember a fun day. Researchers using this design collect all their data at one point, providing a kind of "snapshot" of whatever they're studying.

In a Cross-Sectional Design, researchers look at multiple groups all at the same time to see how they're different or similar.

This design rose to popularity in the mid-20th century, mainly because it's so quick and efficient. Imagine wanting to know how people of different ages feel about a new video game. Instead of waiting for years to see how opinions change, you could just ask people of all ages what they think right now. That's Cross-Sectional Design for you—fast and straightforward.

You'll find this type of research everywhere from marketing studies to healthcare. For instance, you might have heard about surveys asking people what they think about a new product or political issue. Those are usually cross-sectional studies, aimed at getting a quick read on public opinion.

Cross-Sectional Design Pros

So, what's the big deal with Cross-Sectional Design? Well, it's the go-to when you need answers fast and don't have the time or resources for a more complicated setup.

Cross-Sectional Design Cons

Remember, speed comes with trade-offs. While you get your results quickly, those results are stuck in time. They can't tell you how things change or why they're changing, just what's happening right now.

Cross-Sectional Design Uses

Also, because they're so quick and simple, cross-sectional studies often serve as the first step in research. They give scientists an idea of what's going on so they can decide if it's worth digging deeper. In that way, they're a bit like a movie trailer, giving you a taste of the action to see if you're interested in seeing the whole film.

So, in our lineup of experimental designs, if True Experimental Design is the superstar quarterback and Longitudinal Design is the wise elder, then Cross-Sectional Design is like the speedy running back—fast, agile, but not designed for long, drawn-out plays.

7) Correlational Design

Next on our roster is the Correlational Design, the keen observer of the experimental world. Imagine this design as the person at a party who loves people-watching. They don't interfere or get involved; they just observe and take mental notes about what's going on.

In a correlational study, researchers don't change or control anything; they simply observe and measure how two variables relate to each other.

The correlational design has roots in the early days of psychology and sociology. Pioneers like Sir Francis Galton used it to study how qualities like intelligence or height could be related within families.

This design is all about asking, "Hey, when this thing happens, does that other thing usually happen too?" For example, researchers might study whether students who have more study time get better grades or whether people who exercise more have lower stress levels.

One of the most famous correlational studies you might have heard of is the link between smoking and lung cancer. Back in the mid-20th century, researchers started noticing that people who smoked a lot also seemed to get lung cancer more often. They couldn't say smoking caused cancer—that would require a true experiment—but the strong correlation was a red flag that led to more research and eventually, health warnings.

Correlational Design Pros

This design is great at proving that two (or more) things can be related. Correlational designs can help prove that more detailed research is needed on a topic. They can help us see patterns or possible causes for things that we otherwise might not have realized.

Correlational Design Cons

But here's where you need to be careful: correlational designs can be tricky. Just because two things are related doesn't mean one causes the other. That's like saying, "Every time I wear my lucky socks, my team wins." Well, it's a fun thought, but those socks aren't really controlling the game.

Correlational Design Uses

Despite this limitation, correlational designs are popular in psychology, economics, and epidemiology, to name a few fields. They're often the first step in exploring a possible relationship between variables. Once a strong correlation is found, researchers may decide to conduct more rigorous experimental studies to examine cause and effect.

So, if the True Experimental Design is the superstar quarterback and the Longitudinal Design is the wise elder, the Factorial Design is the strategist, and the Cross-Sectional Design is the speedster, then the Correlational Design is the clever scout, identifying interesting patterns but leaving the heavy lifting of proving cause and effect to the other types of designs.

8) Meta-Analysis

Last but not least, let's talk about Meta-Analysis, the librarian of experimental designs.

If other designs are all about creating new research, Meta-Analysis is about gathering up everyone else's research, sorting it, and figuring out what it all means when you put it together.

Imagine a jigsaw puzzle where each piece is a different study. Meta-Analysis is the process of fitting all those pieces together to see the big picture.

The concept of Meta-Analysis started to take shape in the late 20th century, when computers became powerful enough to handle massive amounts of data. It was like someone handed researchers a super-powered magnifying glass, letting them examine multiple studies at the same time to find common trends or results.

You might have heard of the Cochrane Reviews in healthcare . These are big collections of meta-analyses that help doctors and policymakers figure out what treatments work best based on all the research that's been done.

For example, if ten different studies show that a certain medicine helps lower blood pressure, a meta-analysis would pull all that information together to give a more accurate answer.

Meta-Analysis Pros

The beauty of Meta-Analysis is that it can provide really strong evidence. Instead of relying on one study, you're looking at the whole landscape of research on a topic.

Meta-Analysis Cons

However, it does have some downsides. For one, Meta-Analysis is only as good as the studies it includes. If those studies are flawed, the meta-analysis will be too. It's like baking a cake: if you use bad ingredients, it doesn't matter how good your recipe is—the cake won't turn out well.

Meta-Analysis Uses

Despite these challenges, meta-analyses are highly respected and widely used in many fields like medicine, psychology, and education. They help us make sense of a world that's bursting with information by showing us the big picture drawn from many smaller snapshots.

So, in our all-star lineup, if True Experimental Design is the quarterback and Longitudinal Design is the wise elder, the Factorial Design is the strategist, the Cross-Sectional Design is the speedster, and the Correlational Design is the scout, then the Meta-Analysis is like the coach, using insights from everyone else's plays to come up with the best game plan.

9) Non-Experimental Design

Now, let's talk about a player who's a bit of an outsider on this team of experimental designs—the Non-Experimental Design. Think of this design as the commentator or the journalist who covers the game but doesn't actually play.

In a Non-Experimental Design, researchers are like reporters gathering facts, but they don't interfere or change anything. They're simply there to describe and analyze.

Non-Experimental Design Pros

So, what's the deal with Non-Experimental Design? Its strength is in description and exploration. It's really good for studying things as they are in the real world, without changing any conditions.

Non-Experimental Design Cons

Because a non-experimental design doesn't manipulate variables, it can't prove cause and effect. It's like a weather reporter: they can tell you it's raining, but they can't tell you why it's raining.

The downside? Since researchers aren't controlling variables, it's hard to rule out other explanations for what they observe. It's like hearing one side of a story—you get an idea of what happened, but it might not be the complete picture.

Non-Experimental Design Uses

Non-Experimental Design has always been a part of research, especially in fields like anthropology, sociology, and some areas of psychology.

For instance, if you've ever heard of studies that describe how people behave in different cultures or what teens like to do in their free time, that's often Non-Experimental Design at work. These studies aim to capture the essence of a situation, like painting a portrait instead of taking a snapshot.

One well-known example you might have heard about is the Kinsey Reports from the 1940s and 1950s, which described sexual behavior in men and women. Researchers interviewed thousands of people but didn't manipulate any variables like you would in a true experiment. They simply collected data to create a comprehensive picture of the subject matter.

So, in our metaphorical team of research designs, if True Experimental Design is the quarterback and Longitudinal Design is the wise elder, Factorial Design is the strategist, Cross-Sectional Design is the speedster, Correlational Design is the scout, and Meta-Analysis is the coach, then Non-Experimental Design is the sports journalist—always present, capturing the game, but not part of the action itself.

10) Repeated Measures Design

white rat

Time to meet the Repeated Measures Design, the time traveler of our research team. If this design were a player in a sports game, it would be the one who keeps revisiting past plays to figure out how to improve the next one.

Repeated Measures Design is all about studying the same people or subjects multiple times to see how they change or react under different conditions.

The idea behind Repeated Measures Design isn't new; it's been around since the early days of psychology and medicine. You could say it's a cousin to the Longitudinal Design, but instead of looking at how things naturally change over time, it focuses on how the same group reacts to different things.

Imagine a study looking at how a new energy drink affects people's running speed. Instead of comparing one group that drank the energy drink to another group that didn't, a Repeated Measures Design would have the same group of people run multiple times—once with the energy drink, and once without. This way, you're really zeroing in on the effect of that energy drink, making the results more reliable.

Repeated Measures Design Pros

The strong point of Repeated Measures Design is that it's super focused. Because it uses the same subjects, you don't have to worry about differences between groups messing up your results.

Repeated Measures Design Cons

But the downside? Well, people can get tired or bored if they're tested too many times, which might affect how they respond.

Repeated Measures Design Uses

A famous example of this design is the "Little Albert" experiment, conducted by John B. Watson and Rosalie Rayner in 1920. In this study, a young boy was exposed to a white rat and other stimuli several times to see how his emotional responses changed. Though the ethical standards of this experiment are often criticized today, it was groundbreaking in understanding conditioned emotional responses.

In our metaphorical lineup of research designs, if True Experimental Design is the quarterback and Longitudinal Design is the wise elder, Factorial Design is the strategist, Cross-Sectional Design is the speedster, Correlational Design is the scout, Meta-Analysis is the coach, and Non-Experimental Design is the journalist, then Repeated Measures Design is the time traveler—always looping back to fine-tune the game plan.

11) Crossover Design

Next up is Crossover Design, the switch-hitter of the research world. If you're familiar with baseball, you'll know a switch-hitter is someone who can bat both right-handed and left-handed.

In a similar way, Crossover Design allows subjects to experience multiple conditions, flipping them around so that everyone gets a turn in each role.

This design is like the utility player on our team—versatile, flexible, and really good at adapting.

The Crossover Design has its roots in medical research and has been popular since the mid-20th century. It's often used in clinical trials to test the effectiveness of different treatments.

Crossover Design Pros

The neat thing about this design is that it allows each participant to serve as their own control group. Imagine you're testing two new kinds of headache medicine. Instead of giving one type to one group and another type to a different group, you'd give both kinds to the same people but at different times.

Crossover Design Cons

What's the big deal with Crossover Design? Its major strength is in reducing the "noise" that comes from individual differences. Since each person experiences all conditions, it's easier to see real effects. However, there's a catch. This design assumes that there's no lasting effect from the first condition when you switch to the second one. That might not always be true. If the first treatment has a long-lasting effect, it could mess up the results when you switch to the second treatment.

Crossover Design Uses

A well-known example of Crossover Design is in studies that look at the effects of different types of diets—like low-carb vs. low-fat diets. Researchers might have participants follow a low-carb diet for a few weeks, then switch them to a low-fat diet. By doing this, they can more accurately measure how each diet affects the same group of people.

In our team of experimental designs, if True Experimental Design is the quarterback and Longitudinal Design is the wise elder, Factorial Design is the strategist, Cross-Sectional Design is the speedster, Correlational Design is the scout, Meta-Analysis is the coach, Non-Experimental Design is the journalist, and Repeated Measures Design is the time traveler, then Crossover Design is the versatile utility player—always ready to adapt and play multiple roles to get the most accurate results.

12) Cluster Randomized Design

Meet the Cluster Randomized Design, the team captain of group-focused research. In our imaginary lineup of experimental designs, if other designs focus on individual players, then Cluster Randomized Design is looking at how the entire team functions.

This approach is especially common in educational and community-based research, and it's been gaining traction since the late 20th century.

Here's how Cluster Randomized Design works: Instead of assigning individual people to different conditions, researchers assign entire groups, or "clusters." These could be schools, neighborhoods, or even entire towns. This helps you see how the new method works in a real-world setting.

Imagine you want to see if a new anti-bullying program really works. Instead of selecting individual students, you'd introduce the program to a whole school or maybe even several schools, and then compare the results to schools without the program.

Cluster Randomized Design Pros

Why use Cluster Randomized Design? Well, sometimes it's just not practical to assign conditions at the individual level. For example, you can't really have half a school following a new reading program while the other half sticks with the old one; that would be way too confusing! Cluster Randomization helps get around this problem by treating each "cluster" as its own mini-experiment.

Cluster Randomized Design Cons

There's a downside, too. Because entire groups are assigned to each condition, there's a risk that the groups might be different in some important way that the researchers didn't account for. That's like having one sports team that's full of veterans playing against a team of rookies; the match wouldn't be fair.

Cluster Randomized Design Uses

A famous example is the research conducted to test the effectiveness of different public health interventions, like vaccination programs. Researchers might roll out a vaccination program in one community but not in another, then compare the rates of disease in both.

In our metaphorical research team, if True Experimental Design is the quarterback, Longitudinal Design is the wise elder, Factorial Design is the strategist, Cross-Sectional Design is the speedster, Correlational Design is the scout, Meta-Analysis is the coach, Non-Experimental Design is the journalist, Repeated Measures Design is the time traveler, and Crossover Design is the utility player, then Cluster Randomized Design is the team captain—always looking out for the group as a whole.

13) Mixed-Methods Design

Say hello to Mixed-Methods Design, the all-rounder or the "Renaissance player" of our research team.

Mixed-Methods Design uses a blend of both qualitative and quantitative methods to get a more complete picture, just like a Renaissance person who's good at lots of different things. It's like being good at both offense and defense in a sport; you've got all your bases covered!

Mixed-Methods Design is a fairly new kid on the block, becoming more popular in the late 20th and early 21st centuries as researchers began to see the value in using multiple approaches to tackle complex questions. It's the Swiss Army knife in our research toolkit, combining the best parts of other designs to be more versatile.

Here's how it could work: Imagine you're studying the effects of a new educational app on students' math skills. You might use quantitative methods like tests and grades to measure how much the students improve—that's the 'numbers part.'

But you also want to know how the students feel about math now, or why they think they got better or worse. For that, you could conduct interviews or have students fill out journals—that's the 'story part.'

Mixed-Methods Design Pros

So, what's the scoop on Mixed-Methods Design? The strength is its versatility and depth; you're not just getting numbers or stories, you're getting both, which gives a fuller picture.

Mixed-Methods Design Cons

But, it's also more challenging. Imagine trying to play two sports at the same time! You have to be skilled in different research methods and know how to combine them effectively.

Mixed-Methods Design Uses

A high-profile example of Mixed-Methods Design is research on climate change. Scientists use numbers and data to show temperature changes (quantitative), but they also interview people to understand how these changes are affecting communities (qualitative).

In our team of experimental designs, if True Experimental Design is the quarterback, Longitudinal Design is the wise elder, Factorial Design is the strategist, Cross-Sectional Design is the speedster, Correlational Design is the scout, Meta-Analysis is the coach, Non-Experimental Design is the journalist, Repeated Measures Design is the time traveler, Crossover Design is the utility player, and Cluster Randomized Design is the team captain, then Mixed-Methods Design is the Renaissance player—skilled in multiple areas and able to bring them all together for a winning strategy.

14) Multivariate Design

Now, let's turn our attention to Multivariate Design, the multitasker of the research world.

If our lineup of research designs were like players on a basketball court, Multivariate Design would be the player dribbling, passing, and shooting all at once. This design doesn't just look at one or two things; it looks at several variables simultaneously to see how they interact and affect each other.

Multivariate Design is like baking a cake with many ingredients. Instead of just looking at how flour affects the cake, you also consider sugar, eggs, and milk all at once. This way, you understand how everything works together to make the cake taste good or bad.

Multivariate Design has been a go-to method in psychology, economics, and social sciences since the latter half of the 20th century. With the advent of computers and advanced statistical software, analyzing multiple variables at once became a lot easier, and Multivariate Design soared in popularity.

Multivariate Design Pros

So, what's the benefit of using Multivariate Design? Its power lies in its complexity. By studying multiple variables at the same time, you can get a really rich, detailed understanding of what's going on.

Multivariate Design Cons

But that complexity can also be a drawback. With so many variables, it can be tough to tell which ones are really making a difference and which ones are just along for the ride.

Multivariate Design Uses

Imagine you're a coach trying to figure out the best strategy to win games. You wouldn't just look at how many points your star player scores; you'd also consider assists, rebounds, turnovers, and maybe even how loud the crowd is. A Multivariate Design would help you understand how all these factors work together to determine whether you win or lose.

A well-known example of Multivariate Design is in market research. Companies often use this approach to figure out how different factors—like price, packaging, and advertising—affect sales. By studying multiple variables at once, they can find the best combination to boost profits.

In our metaphorical research team, if True Experimental Design is the quarterback, Longitudinal Design is the wise elder, Factorial Design is the strategist, Cross-Sectional Design is the speedster, Correlational Design is the scout, Meta-Analysis is the coach, Non-Experimental Design is the journalist, Repeated Measures Design is the time traveler, Crossover Design is the utility player, Cluster Randomized Design is the team captain, and Mixed-Methods Design is the Renaissance player, then Multivariate Design is the multitasker—juggling many variables at once to get a fuller picture of what's happening.

15) Pretest-Posttest Design

Let's introduce Pretest-Posttest Design, the "Before and After" superstar of our research team. You've probably seen those before-and-after pictures in ads for weight loss programs or home renovations, right?

Well, this design is like that, but for science! Pretest-Posttest Design checks out what things are like before the experiment starts and then compares that to what things are like after the experiment ends.

This design is one of the classics, a staple in research for decades across various fields like psychology, education, and healthcare. It's so simple and straightforward that it has stayed popular for a long time.

In Pretest-Posttest Design, you measure your subject's behavior or condition before you introduce any changes—that's your "before" or "pretest." Then you do your experiment, and after it's done, you measure the same thing again—that's your "after" or "posttest."

Pretest-Posttest Design Pros

What makes Pretest-Posttest Design special? It's pretty easy to understand and doesn't require fancy statistics.

Pretest-Posttest Design Cons

But there are some pitfalls. For example, what if the kids in our math example get better at multiplication just because they're older or because they've taken the test before? That would make it hard to tell if the program is really effective or not.

Pretest-Posttest Design Uses

Let's say you're a teacher and you want to know if a new math program helps kids get better at multiplication. First, you'd give all the kids a multiplication test—that's your pretest. Then you'd teach them using the new math program. At the end, you'd give them the same test again—that's your posttest. If the kids do better on the second test, you might conclude that the program works.

One famous use of Pretest-Posttest Design is in evaluating the effectiveness of driver's education courses. Researchers will measure people's driving skills before and after the course to see if they've improved.

16) Solomon Four-Group Design

Next up is the Solomon Four-Group Design, the "chess master" of our research team. This design is all about strategy and careful planning. Named after Richard L. Solomon who introduced it in the 1940s, this method tries to correct some of the weaknesses in simpler designs, like the Pretest-Posttest Design.

Here's how it rolls: The Solomon Four-Group Design uses four different groups to test a hypothesis. Two groups get a pretest, then one of them receives the treatment or intervention, and both get a posttest. The other two groups skip the pretest, and only one of them receives the treatment before they both get a posttest.

Sound complicated? It's like playing 4D chess; you're thinking several moves ahead!

Solomon Four-Group Design Pros

What's the pro and con of the Solomon Four-Group Design? On the plus side, it provides really robust results because it accounts for so many variables.

Solomon Four-Group Design Cons

The downside? It's a lot of work and requires a lot of participants, making it more time-consuming and costly.

Solomon Four-Group Design Uses

Let's say you want to figure out if a new way of teaching history helps students remember facts better. Two classes take a history quiz (pretest), then one class uses the new teaching method while the other sticks with the old way. Both classes take another quiz afterward (posttest).

Meanwhile, two more classes skip the initial quiz, and then one uses the new method before both take the final quiz. Comparing all four groups will give you a much clearer picture of whether the new teaching method works and whether the pretest itself affects the outcome.

The Solomon Four-Group Design is less commonly used than simpler designs but is highly respected for its ability to control for more variables. It's a favorite in educational and psychological research where you really want to dig deep and figure out what's actually causing changes.

17) Adaptive Designs

Now, let's talk about Adaptive Designs, the chameleons of the experimental world.

Imagine you're a detective, and halfway through solving a case, you find a clue that changes everything. You wouldn't just stick to your old plan; you'd adapt and change your approach, right? That's exactly what Adaptive Designs allow researchers to do.

In an Adaptive Design, researchers can make changes to the study as it's happening, based on early results. In a traditional study, once you set your plan, you stick to it from start to finish.

Adaptive Design Pros

This method is particularly useful in fast-paced or high-stakes situations, like developing a new vaccine in the middle of a pandemic. The ability to adapt can save both time and resources, and more importantly, it can save lives by getting effective treatments out faster.

Adaptive Design Cons

But Adaptive Designs aren't without their drawbacks. They can be very complex to plan and carry out, and there's always a risk that the changes made during the study could introduce bias or errors.

Adaptive Design Uses

Adaptive Designs are most often seen in clinical trials, particularly in the medical and pharmaceutical fields.

For instance, if a new drug is showing really promising results, the study might be adjusted to give more participants the new treatment instead of a placebo. Or if one dose level is showing bad side effects, it might be dropped from the study.

The best part is, these changes are pre-planned. Researchers lay out in advance what changes might be made and under what conditions, which helps keep everything scientific and above board.

In terms of applications, besides their heavy usage in medical and pharmaceutical research, Adaptive Designs are also becoming increasingly popular in software testing and market research. In these fields, being able to quickly adjust to early results can give companies a significant advantage.

Adaptive Designs are like the agile startups of the research world—quick to pivot, keen to learn from ongoing results, and focused on rapid, efficient progress. However, they require a great deal of expertise and careful planning to ensure that the adaptability doesn't compromise the integrity of the research.

18) Bayesian Designs

Next, let's dive into Bayesian Designs, the data detectives of the research universe. Named after Thomas Bayes, an 18th-century statistician and minister, this design doesn't just look at what's happening now; it also takes into account what's happened before.

Imagine if you were a detective who not only looked at the evidence in front of you but also used your past cases to make better guesses about your current one. That's the essence of Bayesian Designs.

Bayesian Designs are like detective work in science. As you gather more clues (or data), you update your best guess on what's really happening. This way, your experiment gets smarter as it goes along.

In the world of research, Bayesian Designs are most notably used in areas where you have some prior knowledge that can inform your current study. For example, if earlier research shows that a certain type of medicine usually works well for a specific illness, a Bayesian Design would include that information when studying a new group of patients with the same illness.

Bayesian Design Pros

One of the major advantages of Bayesian Designs is their efficiency. Because they use existing data to inform the current experiment, often fewer resources are needed to reach a reliable conclusion.

Bayesian Design Cons

However, they can be quite complicated to set up and require a deep understanding of both statistics and the subject matter at hand.

Bayesian Design Uses

Bayesian Designs are highly valued in medical research, finance, environmental science, and even in Internet search algorithms. Their ability to continually update and refine hypotheses based on new evidence makes them particularly useful in fields where data is constantly evolving and where quick, informed decisions are crucial.

Here's a real-world example: In the development of personalized medicine, where treatments are tailored to individual patients, Bayesian Designs are invaluable. If a treatment has been effective for patients with similar genetics or symptoms in the past, a Bayesian approach can use that data to predict how well it might work for a new patient.

This type of design is also increasingly popular in machine learning and artificial intelligence. In these fields, Bayesian Designs help algorithms "learn" from past data to make better predictions or decisions in new situations. It's like teaching a computer to be a detective that gets better and better at solving puzzles the more puzzles it sees.

19) Covariate Adaptive Randomization

old person and young person

Now let's turn our attention to Covariate Adaptive Randomization, which you can think of as the "matchmaker" of experimental designs.

Picture a soccer coach trying to create the most balanced teams for a friendly match. They wouldn't just randomly assign players; they'd take into account each player's skills, experience, and other traits.

Covariate Adaptive Randomization is all about creating the most evenly matched groups possible for an experiment.

In traditional randomization, participants are allocated to different groups purely by chance. This is a pretty fair way to do things, but it can sometimes lead to unbalanced groups.

Imagine if all the professional-level players ended up on one soccer team and all the beginners on another; that wouldn't be a very informative match! Covariate Adaptive Randomization fixes this by using important traits or characteristics (called "covariates") to guide the randomization process.

Covariate Adaptive Randomization Pros

The benefits of this design are pretty clear: it aims for balance and fairness, making the final results more trustworthy.

Covariate Adaptive Randomization Cons

But it's not perfect. It can be complex to implement and requires a deep understanding of which characteristics are most important to balance.

Covariate Adaptive Randomization Uses

This design is particularly useful in medical trials. Let's say researchers are testing a new medication for high blood pressure. Participants might have different ages, weights, or pre-existing conditions that could affect the results.

Covariate Adaptive Randomization would make sure that each treatment group has a similar mix of these characteristics, making the results more reliable and easier to interpret.

In practical terms, this design is often seen in clinical trials for new drugs or therapies, but its principles are also applicable in fields like psychology, education, and social sciences.

For instance, in educational research, it might be used to ensure that classrooms being compared have similar distributions of students in terms of academic ability, socioeconomic status, and other factors.

Covariate Adaptive Randomization is like the wise elder of the group, ensuring that everyone has an equal opportunity to show their true capabilities, thereby making the collective results as reliable as possible.

20) Stepped Wedge Design

Let's now focus on the Stepped Wedge Design, a thoughtful and cautious member of the experimental design family.

Imagine you're trying out a new gardening technique, but you're not sure how well it will work. You decide to apply it to one section of your garden first, watch how it performs, and then gradually extend the technique to other sections. This way, you get to see its effects over time and across different conditions. That's basically how Stepped Wedge Design works.

In a Stepped Wedge Design, all participants or clusters start off in the control group, and then, at different times, they 'step' over to the intervention or treatment group. This creates a wedge-like pattern over time where more and more participants receive the treatment as the study progresses. It's like rolling out a new policy in phases, monitoring its impact at each stage before extending it to more people.

Stepped Wedge Design Pros

The Stepped Wedge Design offers several advantages. Firstly, it allows for the study of interventions that are expected to do more good than harm, which makes it ethically appealing.

Secondly, it's useful when resources are limited and it's not feasible to roll out a new treatment to everyone at once. Lastly, because everyone eventually receives the treatment, it can be easier to get buy-in from participants or organizations involved in the study.

Stepped Wedge Design Cons

However, this design can be complex to analyze because it has to account for both the time factor and the changing conditions in each 'step' of the wedge. And like any study where participants know they're receiving an intervention, there's the potential for the results to be influenced by the placebo effect or other biases.

Stepped Wedge Design Uses

This design is particularly useful in health and social care research. For instance, if a hospital wants to implement a new hygiene protocol, it might start in one department, assess its impact, and then roll it out to other departments over time. This allows the hospital to adjust and refine the new protocol based on real-world data before it's fully implemented.

In terms of applications, Stepped Wedge Designs are commonly used in public health initiatives, organizational changes in healthcare settings, and social policy trials. They are particularly useful in situations where an intervention is being rolled out gradually and it's important to understand its impacts at each stage.

21) Sequential Design

Next up is Sequential Design, the dynamic and flexible member of our experimental design family.

Imagine you're playing a video game where you can choose different paths. If you take one path and find a treasure chest, you might decide to continue in that direction. If you hit a dead end, you might backtrack and try a different route. Sequential Design operates in a similar fashion, allowing researchers to make decisions at different stages based on what they've learned so far.

In a Sequential Design, the experiment is broken down into smaller parts, or "sequences." After each sequence, researchers pause to look at the data they've collected. Based on those findings, they then decide whether to stop the experiment because they've got enough information, or to continue and perhaps even modify the next sequence.

Sequential Design Pros

This allows for a more efficient use of resources, as you're only continuing with the experiment if the data suggests it's worth doing so.

One of the great things about Sequential Design is its efficiency. Because you're making data-driven decisions along the way, you can often reach conclusions more quickly and with fewer resources.

Sequential Design Cons

However, it requires careful planning and expertise to ensure that these "stop or go" decisions are made correctly and without bias.

Sequential Design Uses

In terms of its applications, besides healthcare and medicine, Sequential Design is also popular in quality control in manufacturing, environmental monitoring, and financial modeling. In these areas, being able to make quick decisions based on incoming data can be a big advantage.

This design is often used in clinical trials involving new medications or treatments. For example, if early results show that a new drug has significant side effects, the trial can be stopped before more people are exposed to it.

On the flip side, if the drug is showing promising results, the trial might be expanded to include more participants or to extend the testing period.

Think of Sequential Design as the nimble athlete of experimental designs, capable of quick pivots and adjustments to reach the finish line in the most effective way possible. But just like an athlete needs a good coach, this design requires expert oversight to make sure it stays on the right track.

22) Field Experiments

Last but certainly not least, let's explore Field Experiments—the adventurers of the experimental design world.

Picture a scientist leaving the controlled environment of a lab to test a theory in the real world, like a biologist studying animals in their natural habitat or a social scientist observing people in a real community. These are Field Experiments, and they're all about getting out there and gathering data in real-world settings.

Field Experiments embrace the messiness of the real world, unlike laboratory experiments, where everything is controlled down to the smallest detail. This makes them both exciting and challenging.

Field Experiment Pros

On one hand, the results often give us a better understanding of how things work outside the lab.

While Field Experiments offer real-world relevance, they come with challenges like controlling for outside factors and the ethical considerations of intervening in people's lives without their knowledge.

Field Experiment Cons

On the other hand, the lack of control can make it harder to tell exactly what's causing what. Yet, despite these challenges, they remain a valuable tool for researchers who want to understand how theories play out in the real world.

Field Experiment Uses

Let's say a school wants to improve student performance. In a Field Experiment, they might change the school's daily schedule for one semester and keep track of how students perform compared to another school where the schedule remained the same.

Because the study is happening in a real school with real students, the results could be very useful for understanding how the change might work in other schools. But since it's the real world, lots of other factors—like changes in teachers or even the weather—could affect the results.

Field Experiments are widely used in economics, psychology, education, and public policy. For example, you might have heard of the famous "Broken Windows" experiment in the 1980s that looked at how small signs of disorder, like broken windows or graffiti, could encourage more serious crime in neighborhoods. This experiment had a big impact on how cities think about crime prevention.

From the foundational concepts of control groups and independent variables to the sophisticated layouts like Covariate Adaptive Randomization and Sequential Design, it's clear that the realm of experimental design is as varied as it is fascinating.

We've seen that each design has its own special talents, ideal for specific situations. Some designs, like the Classic Controlled Experiment, are like reliable old friends you can always count on.

Others, like Sequential Design, are flexible and adaptable, making quick changes based on what they learn. And let's not forget the adventurous Field Experiments, which take us out of the lab and into the real world to discover things we might not see otherwise.

Choosing the right experimental design is like picking the right tool for the job. The method you choose can make a big difference in how reliable your results are and how much people will trust what you've discovered. And as we've learned, there's a design to suit just about every question, every problem, and every curiosity.

So the next time you read about a new discovery in medicine, psychology, or any other field, you'll have a better understanding of the thought and planning that went into figuring things out. Experimental design is more than just a set of rules; it's a structured way to explore the unknown and answer questions that can change the world.

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Experimental Research Design-types & process

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Experimental Research Design

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experimental design research methodology

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This chapter addresses the peculiarities, characteristics, and major fallacies of experimental research designs. Experiments have a long and important history in the social, natural, and medicinal sciences. Unfortunately, in business and management this looks differently. This is astounding, as experiments are suitable for analyzing cause-and-effect relationships. A true experiment is a brilliant method for finding out if one element really causes other elements. Also, researchers find relevant information on how to write an experimental research design paper and learn about typical methodologies used for this research design. The chapter closes with referring to overlapping and adjacent research designs.

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Hunziker, S., Blankenagel, M. (2021). Experimental Research Design. In: Research Design in Business and Management. Springer Gabler, Wiesbaden. https://doi.org/10.1007/978-3-658-34357-6_12

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Health impacts of biophilic design from a multisensory interaction perspective: empirical evidence, research designs, and future directions.

experimental design research methodology

1. Introduction

3. research findings, 3.1. bi-sensory, 3.1.1. visual–acoustical, 3.1.2. visual–thermal, 3.1.3. visual–olfactory, 3.1.4. acoustical–thermal, 3.1.5. acoustical–olfactory, 3.1.6. other bi-sensory elements, 3.2. multisensory experience, 4. study design implication, 4.1. study type and subject, 4.2. environmental settings, 4.3. measures, 4.4. study procedure, 5. gaps and future directions, 5.1. beneficial effects of sensory experiences, 5.2. interaction between multisensory exposure to nature, 5.3. subjects heterogeneity and limited generalization, 5.4. study design methodology for multisensory studies, 5.5. the lasting impact of multisensory experiences, 5.6. objective physiological measures, 6. conclusions, author contributions, conflicts of interest.

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Click here to enlarge figure

No.ReferenceSensorySubjectToolExperimental DesignEnvironmental ProcedureMeasuresMain Conclusions
VisualAcoustical ThermalSmell
1Park et al., 2020 [ ] 32
ordinary people
(16 males, 16 females;
age range: 20–39;
half of them were in their 20 s and the other half were in their 30 s).
Recruited from
online study advertisement;
hearing Screening;
and psychometric Screening;
UK
Biometric measures
Questionnaire
Visual:
VR screen (360-degree video)
Acoustical:
headphones
Visual–auditory interaction vs. visual only
Visual:
rural landscape (with or without water features) vs. urban scenes
Auditory:
sound recorded along with the video
1 min baseline clip
1 min stressor clip
1 min recovery clip (experimental exposure)
Responding to questionnaire
Psychological response (verbally respond to the questionnaire):
Tranquility, preference, and pleasantness
for the recovery clips
Perceived restorativeness soundscape scale (PRSS)
Physiological response: two facial electromyography data points (fEMG), heart rate (HR), respiration rate (RR), and electrodermal activity (EDA)
The rural settings had a better recovery when they were presented as visual–audio combined.
Water features led to a greater recovery.
2Hong and Jeon, 2013 [ ] 20
ordinary people
(15 males, 5 females;
age range: 23–34; M : 27.2;
standard deviation: 2.24).
Hearing screening;
consistency test;
South Korea
Questionnaire
Visual:
beam projector
Acoustical:
headphones
Visual-only, audio-only, and visual–auditory interaction
Visual:
images of
streetscapes with a combination of
vegetation and water features (photomontage method)
Auditory:
9 acoustic stimuli were constructed using 4 individual sounds
Continuous experimental exposure while responding to the questionnaireSubjective evaluation:
Preference for each stimulus
Semantic differential test: 12 pairs of adjective attributes
(quiet–noisy, calm–loud, pleasant–unpleasant, comfortable–uncomfortable, open–closed, wide–narrow, stable–unstable, harmonious–disharmonious, ordered–disordered, various–monotonous, distinct–ordinary, and natural–artificial.)
Increases in greenery from trees or bushes can improve
streetscapes.
Bird sounds were more useful
for enhancing soundscape quality compared to water.
The contribution of acoustic comfort to the overall impression was more significant than visual factors with a high level of road traffic noise.
3Jahncke et al., 2015 [ ] 40
(49 students ;
22 males, 27 females;
M : 24.1).
Recruited from the University of Gävle.
Hearing Screening;
UK
Questionnaire
Visual:
screen
Acoustical:
headphones
Visual:
open plan office and urban nature
Auditory:
natural sound, quiet, broadband noise, office noise
Fatigue scenario
Control and background questions
1 min exposure to each setting (8 settings)
Statement questions
Control and background questions
Perceived restorativeness scale (PRS)
Restoration likelihood
attitude toward the presented setting
Natural sound positively influenced evaluations of the natural setting compared to the office settings.
There are significant interactions between acoustic and visual stimuli were found for all measures.
4Ma and Shu, 2018 [ ] 75
(Study1: 30, Study2: 15, Study3: 30;
male/femal = 1:1;
M : 25).
Recruited from Tianjin University;
hearing screening;
working status and stress level assessment;
Tianjin, China

Biometric measures
Questionnaire
Cognitive test
Visual:
screen
Acoustical:
headphones
Auditory-only (types and sequences) vs. visual–auditory interaction
Visual:
open plan office with and without natural elements
Auditory:
flowing water sound and urban noise
Within-subject study
5 min introduction of stress and attentional fatigue
2 min measure original status
3 min restoration period
2 min measurements of restorative effects
2 min rest (then next experiment unit)
Physiological responses: blood pressure (BP) and heart rate (HR)
Psychological experience: 3 emotional states (tension, fatigue, and annoyance)
Cognitive performance: task performance
Soundscape elements had an apparent positive effect on tiredness, restoration, and annoyance reduction.
Sound elements had a greater effect on psychological
restoration compared with visual scenes.
5Sun et al., 2018 [ ] 68
(40 males, 28 Females; M = 27.9, SD = 5.05, range: 20–46;
48 obtained a master’s degree or higher).
Hearing screening;
Belgium
Questionnaire
Visual:
screen
Acoustical:
speaker
Auditory only vs. visual–auditory interaction
Visual:
4 scenarios, airport car, restaurant, aircraft, and city park
Auditory:
6 sound groups, the sound was recorded along with the scenario

Part 1: Audio: 3 sound contents
Part 2: Video: 3 sound contents
(10 min, experiments were repeated for four days for different scenes)
Preference: which of the 3 items sounds most different from the other two?Audiovisual aptitude may affect the appraisal of the living environment.
6Abdalrahman and Galbrun, 2020 [ ] 31
(16 males, 15 females; range: 24–60, M ¼ 36.3,
SD ¼ 9.3).
Participants were postgraduate students and staff members of Heriot-Watt University who worked in open-plan offices;
hearing screening;
UK
Questionnaire
Visual:
screen
Acoustical:
headphones
Audio-only vs. audio–visual interaction
(Detailed information about Exp 1 is not discussed here).
Visual:
still images from the animation of the water feature (6 settings)
Auditory:
water mask: recording of 6 water features (the 20 s each); speech recording: open-plan office
Part 1 (30–35 min) [15 pairs of comparison]:
Audio only/visual audio (7 s underwater sound—a 4-step cascade (CA), 1 s silence, and 7 s another underwater sound—a 37-jet fountain (FTW)
Part 2 (5–10 min): [6 settings]
Audio only/visual audio (7 s unmasked voice, 1 s gap, and 7 s voice masked by water sound)
Rate perception changes
Preference of waterscape
Sound perception changes
The introduction of a water feature improved the perception of the sound environment and adding visual stimuli improved perception by up to 2.5 times.
7Galbrun and Calarco, 2014 [ ] 38
(19 males, 19 females; range: 24–47; M : 30.1; standard deviation: 4.47).
Hearing screening;
consistency test;
cultural groups
UK
Questionnaire
Visual:
screen
Acoustical:
headphones
An audio-only vs. visual-only vs. visual–auditory interaction
Visual: photo montages with different water features and the same natural background
Auditory:
10 water sounds and road traffic noise
Pair comparison:
Audio-only test: a select sound that is more peaceful and relaxing [20 min] + quality analysis of water sound [20—30 min]
Visual-only test: the image that prefers to look at [20 min] + rate water feature display [5–10 min]
Audiovisual test: feature they prefer in terms of peacefulness and relaxation [20 min]+ rate water feature display [5–10 min]
Pair comparison
Sound qualities: semantic assessment, categorization, and evocation
Water features’ displays as man-made, natural, or neither
Equal attention should be given to the design of both visual and acoustical stimuli.
Natural-looking features tended to increase preference scores compared to audio-only
paired comparison scores.
8Liu et al., 2023 [ ] 28
(14 males, 14 females).
Recruited from
Qingdao University;
psychiatric screening;
climate adaptation screening;
unhealthy behaviors such as alcohol and tobacco addiction screening;
BMI screening;
Qingdao, China
Biometric measures
Visual:
slides
Acoustical:
stereophonic loudspeaker
An audio-only vs. visual-only vs. visual–auditory interaction
Visual:
natural scenes (green trees and forests)
Auditory:
the sound of naturally running water, with a frequency of
400–500 Hz and a sound level of 40–50 dB
10 min baseline measuring stage
10 min stress induction stage (continuous high-frequency noise)
20 min stress recovery stage (the auditory and the visual-auditory stimuli, respectively)
Continuous electrocardiogram (ECG) data
Heart rate variability analysis: mean heart rate,
the root mean square of successive differences (RMSSD) between normal heartbeats, the low-frequency and high-frequency power ratio (LF/HF)
The visual and visual–auditory environment produced a better acute recovery effect.
In longer recovery time, the auditory restorative environment might produce the most pronounced stress-recovery effects, followed by the visual restorative environment.
9Aristizabal et al., 2021 [ ] 37
(Cohort 1 (6 females,
7 males, M = 41.85);
Cohort 2 (5 females,
8 males, M = 33.62);
Cohort 3 (8 females,
4 males, M = 33.73)
range(18–60);).
Hearing and vision screening;
cardiovascular disease, psychiatric, stress, depression, drug, and alcohol dependence screening;
health assessment;
duration of residence screening ;
Minnesota, USA
Biometric measures
Questionnaire
Cognitive test
Visual:
digital screens
Acoustical: speakers
An audio-only vs. visual-only vs. visual–auditory interaction
Visual:
indoor plants and rotating, digital projections of nature including fractal imagery and canopy-type plants
Auditory:
reminiscent of the natural, regional environment including blowing wind, trickling water, and sounds produced by regional fauna
Pair comparison:
Baseline office environment with no environmental aspects (2 weeks)
Introducing only visual biological conditions (8 weeks)
Introducing only auditory biological conditions (8 weeks)
Introducing visual and auditory biological conditions (8 weeks)
Physiological indicators of stress, including changes in heart rate and electrodermal activity
Feelings of stress, environmental satisfaction, perceived productivity, mood, and connectedness to nature
Objective indicators of cognitive performance
Working memory test, inhibition control, and task-switching
Immersive biophilic
environments can improve occupants’ satisfaction and cognitive performance while reducing stress.
Highlight the need to consider non-visual factors in biophilic design.
10Kulve et al., 2018 [ ] 35
(All females; age range: 18–30; M : 22.2).
Recruited via advertisements at the university and the
website digi-prik.nl.
BMI screening;
inclusion criteria: Caucasian females, generally healthy.
Exclusion criteria: color blindness, ocular pathologies, medication use, pregnancy, hypertension, general feeling of illness on the day of the experiment, (history of) cardiovascular diseases, and contraindication of the telemetric pill.
The Netherlands
Biometric measures
Questionnaire
Visual:
luminance level and color temperature (electrical lighting)
Thermal:
room temperature
Visual:
Study 1: Dim (5 lux) and Bright (1200 lux) with constant color temperature (4000 K)
Study 2:
Color temperature (2700 K and 5800 K) with constant luminance level (50 lux)
Thermal:
baseline temperature 29 °C, low temperature 26 °C, and high temperature 32 °C
For both studies:
30 min baseline measure (29 °C)
15 min break
75 min 1st block (26 or 32 °C)
15 min break
75 min 1st block (29 °C)
15 min break
75 min 1st block (26 or 32 °C)
Questionnaire for thermal and visual perception:
Thermal: “thermal comfort”, “thermal sensation”, “preferred temperature change”, “self-assessed
shivering”, and “self-assessed sweating”
Visual: “perceived light intensity”, “perceived light color”, “visual comfort”, “preferred light intensity change”, and “preferred light color change”
Body temperature, skin temperature: 26 body sites; core temperature
Energy expenditure: oxygen consumption and carbon dioxide production
Visual perception and thermal perception affect each other.
Higher visual comfort levels were correlated with higher thermal comfort votes.
Thermal discomfort can be partly compensated by lighting that results in a higher perceived visual comfort.
11Chinazzo et al., 2019 [ ] 84
(42 males, 42 females
age range: 18–30).
Recruited from the subject pool of the Universities.
Vision screening;
inclusion criteria
(age 18–30 years old, no abuse of alcohol or use of drugs, full-color vision, generally healthy, French-speaking–mother tongue or C2 level, BMI between 18 and 25 kg/m , no visual or motor abnormalities).
Lausanne, Switzerland
Biometric measures
Questionnaire
Visual:
luminance level (daylighting)
Thermal:
room temperature
Visual:
daylight illuminance (low ~130 lx, medium ~600 lx, and high ~1400 lx)—change filter
Thermal:
3 temperature levels (19, 23, and 27 °C) (each participant experiences one T)
For each room temperature
45 min pre-test phase
10 min break, change filter
30 min daylight exposure 1
10 min break, change filter
30 min daylight exposure 2
10 min break, change filter
30 min daylight exposure 3
Subjective perception ratings:
4 types of thermal perception:
thermal state (thermal sensation, comfort, and preference) and thermal ambiance (thermal acceptability).
and overall perception
Evaluate overall comfort
The reason for the discomfort
Physiological measurements: skin temperature
Cross-modal effects of daylight on thermal responses occurred, but only at a psychological level rather than at a physiological one.
Daylight affected only thermal evaluations, not thermal sensation.
12Ko et al., 2020 [ ] 86
(43 males, 43 females;
age range: >18).
Recruited from the University of California.
Vision screening;
sleep disorders screening;
California, USA
Biometric measures
Questionnaire
Cognitive test
Visual:
view content (natural view)
Thermal:
room temperature
Visual:
with or without a window view
Thermal:
28 °C (slightly warm condition)
For each window setting:
15 min setup
5 min survey
10 min creativity tests
5 min break in chamber
25 min cognitive tests
5 min survey
10 min break in the reception area
Thermal perception: thermal sensation, comfort, acceptability, and pleasure
Mean skin temperature
Emotion: circumplex model
Cognitive performance: working memory, concentration, short-term memory, spatial planning, and creativity performance test
Eye symptoms and perceived stress level
People close to a window can tolerate small thermal comfort deviations.
Window view can enhance positive emotions, reduce negative emotions, and improve workers’ productivity.
13Song et al., 2019 [ ] 21
(All females;
M : 21.1 ± 1.0 years).
Recruited from a Japanese university.
Exclusion criteria: smoking, treatment of diseases, menstrual period;
Japan
Biometric measures
Questionnaire
Visual:
screen
Scent:
essential oil
odor bag
diffuser
Visual-only vs. olfactory-only vs. visual–olfactory
interaction
Visual:
a photograph view of a forest landscape of Hinoki cypress trees (Chamaecyparis obtusa, a type of conifer)
Olfactory:
hinoki cypress leaf oil
The participant remained sitting, and her physiological responses were continually measured.
60 s (the rest period)
viewed a gray Background
90 s (stimuli) the visual, olfactory, combined visual and olfactory
Subjective indices evaluation
Near-infrared time-resolved spectroscopy
(oxy-Hb concentration in the participant’s left and right prefrontal cortex)
Heart rate variability and heart rate
The HF component of HRV reflects parasympathetic nervous activity and the ratio of LF to HF reflects sympathetic nervous activity
Modified semantic differential method
The forest-related stimuli induced a significant decrease in the oxy-Hb concentration in the prefrontal cortex and a significant decrease in sympathetic nervous activity.
Significant increases in subjective feelings related to the terms “comfortable”, “relaxed”, “natural”, and “realistic”.
The combined visual and olfactory stimuli demonstrated an additive effect.
14Li et al., 2024 [ ] 48
(24 males, 24 females;
M : 22.66 ± 1.82).
Recruited from college.
Vision and olfaction screening;
no prior history of mental, cardiovascular, or allergic diseases;
anxiety and depression screening;
BMI.
No significant differences among the four groups in terms of gender ratio, age, height, weight, or body mass index (BMI);
Beijing, China
Biometric measures
Questionnaire
Cognitive test
Visual:
plant
Scent:
plant
breathing mask
Visual-only vs. olfactory-only vs. visual–olfactory interaction
Visual:
2 (plant present vs. absent)—Coriander
Olfactory:
2 (scent present vs. absent)—Coriander scent
All tests were in the same period of time (14:00–16:00)
5 min rest
(baseline values):
completed saliva collection, self-reported questionnaire, and cognitive tests
30 min (stimulation)
5 min rest: completed saliva collection, and self-reported questionnaire
30 min (stimulation)
5 min rest: completed saliva collection, self-reported questionnaire, and cognitive tests
Psychological indicators: the Profile of Mood States (POMS) questionnaire;
Electrophysiological indicators: electrocardiogram (ECG), electrodermal activity (EDA), and electroencephalogram (EEG);
Salivary biochemical indicators: salivary stress marker (cortisol), proinflammatory cytokines, and untargeted metabolomics;
Cognitive performance: psychomotor vigilance task (PVT) and spatial working memory span task (SWMS).
The various types of sensory stimuli associated with coriander plants exhibited different intervention effects on mood and cognition.
The combined stimulus demonstrated better effects compared to the single-sensory stimulus.
All three stimuli—visual, olfactory, and combined—induced spontaneous neural oscillations associated with relaxation or cognitive function, and significant changes occurred in metabolic pathways related to antidepressant, anti-inflammatory, or neuroprotective effects.
It appeared that visual stimuli elicited a greater response from the nervous system, while olfactory stimuli elicited a greater response from the endocrine and immune systems.
15Yang and Moon, 2019 [ ] 54
(25 males, 29 females;
M : 22 ± 1.9).
Recruited from university.
Hearing screening;
South Korea
Questionnaire
Acoustical:
water sound (speaker)
Thermal:
room temperature
Acoustical:
2 types and 4 levels of water sound (45, 50, 55 dBA, and 60 dBA)
Thermal:
18 °C (cool), 24 °C (neutral), and 30 °C (warm)
For each room temperature:
30 min thermal adaptation
30 min experimental period [25 s sound stimulus + 15 s response (36 sound stimulus)]
Negative acoustic attributes and positive acoustic attributes
Acoustic comfort, thermal comfort, and overall comfort
Room temperature affected both thermal perception and acoustic perception.
Water sounds affected not only acoustic perception but also thermal and overall indoor environmental comfort.
16Mattila and Wirtz, 2001 [ ] 247
(Female: 75%, less than
20 years old: 65%).
Subjects were anyone entering the store who agreed and completed the questionnaire;
USA
Questionnaire
Acoustical:
sound system
Scent:
diffuser
Acoustical:
3 categories (no music/low arousal music/high arousal music)
Olfactory:
3 categories (no scent/low arousal scent/high arousal scent)—Lavender (low arousal) and Grapefruit (high arousal)
In retail
Pretest of scent and sound
15 min pre-scent of the store
3 shifts (10:30 a.m.–12:30 pm, 2:00 p.m.–4.00 p.m., and 5:00 p.m.–7:00 p.m.)
Randomly select customers leaving the store
Emotional response: arousal dimension and pleasure dimension
Approach–avoidance behavioral responses
The extent of impulse buying
Environment evaluation
When ambient scent and music are congruent with each other in terms of their arousing
qualities, consumers rate the environment significantly more positive.
17Fenko and Loock, 2014 [ ] 117
(28 males, 89 females;
M : 47.92;
ranged: 14-88).
Recruited from the patients of plastic surgeon Dr. Abdul Yousef at the Elizabeth Hospital in Recklinghausen (Germany).
Germany
Questionnaire
Acoustical:
CD player
Scent:
diffuser
Acoustical:
2 (music present vs. absent)—instrumental music with nature sounds
Olfactory:
2 (scent present vs. absent)—Lavender scent
In the waiting room of a German plastic surgeon:
Pretest of scent and sound
Before the appointment: the demographic questions, evaluation of anxiety, and waiting environment
After the appointment: objective and perceived waiting time and manipulation check questions about perceived scent and music
The level of anxiety (Clinical Anxiety Scale and STAI)
Evaluation of the waiting environment (Physical Environment Quality Scale)
Perceived waiting time duration
Objective waiting time
When used separately, each of the environmental factors, music and scent, significantly reduced the level of the patient’s anxiety compared to the control condition.
The combination of scent and music was not effective in reducing anxiety.
18Morrin and Chebat, 2005 [ ] 774
(Range: >18).
Recruited from the mall intercept procedure.
Montreal, Canada
Questionnaire
Acoustical:
mall speaker
Scent:
diffuser
Acoustical:
(music present vs. absent) slow tempo music
Olfactory:
(scent present vs. absent) citrus scents
In suburban shopping malls:
Pretest of scent and sound
Poster for participants’ recruitment
Questionnaire after shopping
Perceived quality of products
The mood was measured with the first 2 dimensions of Mehrabian and Russell’s (1974) PAD scale
The environmental quality of the mall was assessed based on Fisher’s (1974) scale
Atmospheric cues such as music and scent were more effective at enhancing consumer response when they were congruent with individuals’ affectively or cognitively oriented shopping styles.
19Ba and Kang, 2019 [ ] 168
(54.8% females,
M = 22 (SD = 2.6; min = 18; max = 27)).
Recruited from
universities via the Internet and by personal contacts.
Audition and olfaction screening;
no mental illness; and not pregnant.
China
Questionnaire
Acoustical: loudspeaker
Scent:
essential oils and perfume
Acoustical:
3 types (birds, conversation, and traffic)
Olfactory:
4 types (lilac, osmanthus, coffee, and bread)
In a sound insulation chamber:
Pretest of scent and sound
Sound evaluation segment; 9 audios, 40 s each
Odor evaluation segment; 12 odors, 40 s each
Overall evaluation segment
40 s each
5 min ventilation in between for odor and overall evaluation segments
Acoustical comfort, sound preference, sound familiarity, and subjective loudness
Olfactory comfort, odor familiarity, and subjective intensity
Overall comfort
In the presence of birdsong and low-volume sound, overall comfort and congruency are unaffected by odor.
For other combinations of sound and odor, with the increase in concentration, the overall evaluation gradually improves.
A positive sensory stimulus can improve the evaluation of perception through other senses, while a negative sensory stimulus has the opposite effect.
There is a masking effect between audition and olfaction.
20Chang et al.,
2023 [ ]
81
(23 males, 58 females;
age range: 18–26).
Recruited online in advance;
olfaction screening;
neither non-smokers nor drug users;
have lived locally for more than one year;
all volunteers’ clothing insulation ranged from
0.16 to 0.72 clo;
Xi’an, China
Biometric measures
Questionnaire
Thermal:
outdoor environment
Scent:
essential oils
nebulizer
Thermal:
3 typical spaces
The open square (OS) is paved with granite, devoid of vegetation, and unshaded by buildings.
The tree-shaded space (TS) is shaded by beeches and its surface is composed of cement pavement and a grass lawn
The landscape pavilion (LP) is surrounded by vegetation
Olfactory:
Lavandula
officinalis, Rosa rugosa, and Mentha canadensis
All 3 fragrance stimuli were applied in each measured site for 3 experimental combinations
15 min of adapting to the ambient temperature and completing the first questionnaire
Experience fragrance stimuli and were asked to complete the second questionnaire from 3 to 10 min of scent exposure
15 min later, volunteers completed the third questionnaire
Repeated the described process until they had visited all sites and experienced all fragrance stimuli
Electroencephalogram (EEG) measures
Positive and Negative Affect Schedule (PANAS)
Thermal perception vote (thermal sensation vote (TSV) and thermal comfort vote (TCV))
Fragrance perception vote (fragrance sensation vote (FSV), fragrance pleasantness vote (FPV), and fragrance comfort vote (FCV))
Physiological equivalent temperature (PET) and mean TSV (MTSV)
Improving olfactory comfort can partially relieve thermal discomfort caused by high Ta in summer.
Fragrance comfort and fragrance pleasure were improved with an increase in thermal comfort. Exposed to R. rugosa and L. officinalis, thermal discomfort may produce a “revenge effect” on fragrance comfort, resulting in fragrance discomfort.
Fragrance stimuli increased the beta-band when 30.80 °C ≤ PET < 44.53 °C. When 44.53 °C ≤ PET < 58.27 °C, the alpha-band decreased significantly due to fragrance stimuli. Under different PETs, the relative theta-band in all cerebral cortex zones changed significantly, and the wave band was most significantly influenced by olfactory stimuli.
21Yang and Moon, 2019 [ ] 60
(30 males, 30 females).
Recruited from university;
vision and hearing screening;
they were asked to wear a clothing ensemble of nearly 0.75 clo according to the ASHRAE Standard 55–2004.
South Korea
Biometric measures
Visual:
fluorescent lighting
Acoustical: loudspeaker
Thermal:
room temperature
Visual:
3 illuminance level
Acoustical:
4 types of sound (babble, fan, music, and water) with 4 sound levels
Thermal:
20, 25, and 30 °C
3 thermal sessions:
30 min of adaptation period
15 min of response [for each sound, 25 s stimulus, 50 s response]
20 min of wash-out period for each illuminance level (3 illuminance levels)
Acoustic comfort
Thermal comfort
Visual comfort
Indoor environmental comfort
[using an 11-point numeric scale recommended by ISO 15666] [ ]
The effect of acoustic factors was the greatest on indoor environmental comfort, followed by room temperature and illuminance.
22Du et al., 2023 [ ] 458
(Age range: >60)
Recruited from the field;
vision and hearing screening;
Xi’an, China
Questionnaire
Visual:
outdoor view
Acoustical:
loudspeaker
Thermal:
outdoor temperature
Visual:
Visible green index (VGI)
Acoustical:
5 common types of stimulating sound (conversation, birdsong, traffic sound, dance music, and traditional opera)
3 ranges LAeq, low (40–45 dBA), medium (50–55 dBA), and high LAeq (60–65 dBA)
Thermal:
4 selected spaces: square adjacent to water (WS); tree-shaded square (TS); landscape pavilion (LP); open square (OS);
9:00–11:30, 12:30–15:00, 15:30–18:00
15 min of random type of sound stimulation and fill out the questionnaire after
Transfer to the next field and repeat 5 times until listening to all types of sounds
Meteorological parameters, illumination intensity (LUX)
Sound types (STP)
A weighted equivalent continuous sound pressure level (LAeq)
Sky view factor (SVF)
Visible green index (VGI)
Thermal sensation vote (TSV), thermal comfort vote (TCV), acoustic sensation vote (ASV), acoustic comfort vote (ACV), sunlight sensation vote (SSV), visual comfort vote (VCV), and overall comfort vote (OCV)
When PET was above 43.80 °C, the elderly felt thermally uncomfortable. Older adults perceived traffic sound as acoustically uncomfortable when LAeq was higher than 66.1 dBA. A higher VGI decreased the sensitivity of respondents to LUX.
TSV and TCV were susceptible to the acoustic and visual environments. The influence of the visual environment and PET on ASV and ACV were not significant.
There was a significant correlation between PET and SSV.
Acoustic and thermal comfort had a one-vote veto tendency relative to overall comfort but no absolute veto power.
Thermal comfort was the most important factor affecting overall comfort in summer while acoustic comfort was the most important in spring.
A binary logistic regression to predict the overall comfort of elderly adults had 84.7% accuracy, indicating a good performance.
23Sona et al., 2019 [ ] 122
(58 males, 64 females;
M = 22.69, SD = 2.23).
Recruited from German students.
No allergies to the scents used.
Germany

Biometric measures
Visual:
LED screen
Acoustical:
LED screens with speakers
Scent:
dispenser
Visual:
an artificial window,
Acoustical:
consisting of 3 high-resolution LED screens with speakers
Olfactory:
a scent composed of
rosewood, geranium, ylang-ylang, olibanum (frankincense), and hyssop in the natural outdoor condition and composition of rosewood and cardamom in the built indoor condition
The 5 conditions are as follows:
(1) Control, (2) Nature, (3) Lounge, (4) Scented nature, and (5) Scented lounge
50 min depletion phase
15-min restoration phase and fill in the questionnaire
Post-restoration phase
Perception of the space
Pleasantness of window view, sound, and odor
Perceived Restorativeness Scale
Personal resources
Fatigue, mood, and arousal
Analyses showed that the subarachnoid hemorrhage early brain edema score (SEBEs)
simulating either a natural or a lounge environment was perceived as more pleasant and restorative (fascination/being away) than a standard break room, which in turn facilitated the recovery of personal resources (mood, fatigue, and arousal).
24Marcus et al., 2019 [ ] 154
(Age range: 18-50;
city (n = 50, 28 females, 22 males, M : 27);
park (n = 52, 26 females, 26 males, M : 28);
forest (n = 52, 28 females, 24 males; M : 27)).
Recruited from Stockholm (about 1.5 million inhabitants) where they are presumably exposed to a higher degree of the city.
Vision, hearing, and olfaction screening;
inclusion criteria comprised
self-declared health, not pregnant, and not using prescription medication.
Stockholm, Sweden
Biometric measures
Questionnaire
Visual:
2D 360° virtual reality photo
VR mask (Oculus Rift)
Acoustical:
headphones
Scent:
a custom-built nine-channel air-dilution olfactometer
Visual:
a densely built-up urban area, a park, or a forest
Acoustical:
city noise: traffic; park noise: one bird; forest noise: nine bird species and the sound of a slight breeze)
Olfactory:
city odors: diesel, tar, and gunpowder; park odors: grass; forest odors: 2 evergreen species and mushroom
30 seconds baseline measurement
150 s stress induction period (shock at 40, 50, 70, 100, and 150 s).
180 s recovery period
The average perceived pleasantness
Physiological stress test (SCL–measures)
Stress Sensitivity Scale
SCL (skin conductance level)
The park and forest, but not the urban area, provided significant stress reduction.
High pleasantness ratings of the environment were linked to low physiological stress responses for olfactory and auditory but not for visual stimuli.
Olfactory stimuli may be better at facilitating stress reduction than visual stimuli.
25Qi et al., 2022 [ ] 308
(13% male;
M : 22.92 (SD = 2.20;
Range: 18–31).
Recruited from a single college campus.
Vision, hearing, and olfaction screening;
Shaanxi, China
Biometric measures
Questionnaire
Visual:
360° virtual reality photo
Acoustical:
mini wireless speakers
Scent:
odor sensor
Birdsong only vs. birdsong + photo (4 types)/odor (4 types) vs. birdsong + photo + congruent odor (4 types)
Visual:
a white wall as the control; short-cut lawn; rose garden; osmanthus tree garden;
pine forest
Acoustical:
Birdsong:
downloaded from the open sources on the
Internet
Streptopelia decaocto (500–800 Hz); riolus chinensis (1 k-3 kHz);
Passer montanus (3 k-4 k Hz); Chloris sinica (4 k-6 k Hz); Garrulax canorus (2 k-6 k Hz)
Olfactory:
leaves from the lawn; flowers of rose bushes; flowers of osmanthus trees; leaves (pine needles) of pine trees
5 min introduction and questionnaire (part 1)
5 min relaxation
1 min baseline
2 min stimulation
Questionnaire (part 2-4)
5 min rewards distribution
Ventilation
ST (skin temperature), SCL (skin conductance level), and EEG (electroencephalogram)
STAI-S (the state version of the State-Trait Anxiety Inventory)
Semantic differentials (SDs) survey concerning the overall quality evaluation of the environment (overall attraction, overall harmony, and overall preference)
Integrating visual stimuli of birdsong improved physiological restoration and the overall perceived quality evaluation but held no psychological effect.
Introducing olfactory stimuli of birdsong had an adverse restoration physiologically and no significant effect on psychological restoration and the overall preference but enhanced the perceived overall feelings of attraction to the landscape and a sense of overall harmony.
Introducing a combination of visual–olfactory stimuli led to increased physiological restoration (only for β-EEG) and overall perceived quality evaluation but also had no significant effect psychologically.
26Zhong et al., 2022 [ ] 172
(78 males, 94 females;
M : 21).
Recruited from the Architecture Department of Chongqing University.
Normal hearing and a basic knowledge of soundscapes and
landscapes.
Chongqing, China
Questionnaire
Visual/Acoustical/Scent:
outdoor environment
Sense walking
Visual/Acoustical/Olfactory:
seven waterfront spaces in mountainous cities (WSMCs) in Chongqing were randomly selected as the study areas, namely, Jiangbeizui (JB), Shacixiang (SC), Chaotianmen Square (CT), CBD Riverside Park (CB), Liziba Park (LZ), Jiulongpo Park (JL), and Nanbin Park (NB)
A researcher walking alone or with one or more participants
Each participant spent 5 min at each of the walking points to evaluate the soundscape quality and fill out the questionnaire
List all of the sound sources they noticed (referred to the suggestions in ISO/TS 12913-2: 2018 [ ]); soundscape comfort degree (SCD)
Visual environment comfort degree (VECD); visual environment natural degree (VEND); visual environment diversity degree (VEDD)
Smell environment comfort degree (SECD); name the main odors II
In terms of visual elements, the proportions of paved ground, pedestrians, and buildings had negative effects on the soundscape, while those of the sky, water, and natural terrain had positive effects.
High visual and smell environment quality can enhance soundscape evaluations, although the smell environment had a greater impact on the SCD than the visual environment in WSMCs.
ProjectN(Subject) and M:F and Mean Age and TypeReferenceRemark
Visual
Acoustical
20–4032(16:16)30 Ordinary peoplePark et al., 2020 [ ]
20(15:5)27.2 Ordinary peopleHong and Jeon, 2013 [ ]
40(22:27)24.1 StudentsJahncke et al., 2015 [ ]
30; 15; 30
(1:1)
25StudentsMa and Shu, 2018 [ ]
31(16:15)27.9 Ordinary peopleAbdalrahman and Galbrun, 2020 [ ]
38(19:19)36.3 Students and staffsGalbrun and Calarco, 2014 [ ]
28(14:14)30.1 Ordinary peopleLiu et al., 2023 [ ]
37(18:19)/Students Aristizabal et al., 2021 [ ]
68(40:28)30–40Ordinary peopleSun et al., 2018 [ ]Increase the statistical power for subgroup analysis in terms of gender, age, and education
Visual
Thermal
Study 1: 19
Study 2: 16
All females
22.2 Students and ordinary peopleKulve et al., 2018 [ ]All participants went through three room-temperature settings
84(42:42)18–30 StudentsChinazzo et al., 2019 [ ]Each participant only experienced one out of three temperature levels
86(43:43)/StudentsKo et al., 2020 [ ]Compare the window and windowless environments at the same room temperature
Visual
Olfactory
21 All females21.1 StudentsSong et al., 2019 [ ]
48(24:24)22.7 StudentsLi et al., 2024 [ ]
Acoustical
Thermal
54(25:29)22 StudentsYang and Moon, 2019 [ ]Participants underwent three experiments
Acoustical
Olfactory
247(1:3)less 20>
65%
Ordinary peopleMattila and Wirtz, 2001 [ ]Field studies can easily recruit participants, as anyone stepping into the test area could be a candidate
117(28:89)47.9PatientsFenko and Loock, 2014 [ ]
774(/)/ShoppersMorrin and Chebat, 2005 [ ]
168(76:92) 22Students and ordinary peopleBa and Kang, 2019 [ ]Laboratory study
Thermal
Olfactory
81(23:58)18-26Ordinary peopleChang et al., 2023 [ ]Field study
Visual
Acoustical
Thermal
60(30:30)/Students Yang and Moon, 2019 [ ]Participants underwent three experiments
458(/)>60The elderlyDu et al., 2023 [ ]Field study
Visual
Acoustical
Olfactory
122(58:64)22.69Students Sona et al., 2019 [ ]Each participant was exposed to a multisensory environment
154(82:72)27/28Ordinary peopleMarcus et al., 2019 [ ]
308(40:268)22.92Students Qi et al., 2022 [ ]
172(78:94)21Students Zhong et al., 2022 [ ]Field study (sense walking)
Types of ElementsContentReferenceEnvironmental Settings
VisualNature scenery or natural elements Park et al., 2020 [ ]; Hong and Jeon, 2013 [ ]; Jahncke et al., 2015 [ ]; Ma and Shu, 2018 [ ]; Sun et al., 2018 [ ]; Abdalrahman and Galbrun, 2020 [ ]; Galbrun and Calarco, 2014 [ ]; Ko et al., 2020 [ ]; Sona et al., 2019 [ ]; Du et al., 2023 [ ]; Zhong et al., 2022 [ ]
Pictures of landscapes or urban nature Park et al., 2020 [ ]; Hong and Jeon, 2013 [ ]; Jahncke et al., 2015 [ ]; Sun et al., 2018 [ ]; Liu et al., 2023 [ ]; Aristizabal et al., 2021 [ ]; Song et al., 2019 [ ]; Marcus et al., 2019 [ ]; Qi et al., 2022 [ ]
Photomontages with different natural featuresAbdalrahman and Galbrun, 2020 [ ]; Galbrun and Calarco, 2014 [ ]
Video sequence of a park in the natural outdoor conditionSona et al., 2019 [ ]
Greenery existing in offices, such as plants and window viewMa and Shu, 2018 [ ]; Ko et al., 2020 [ ]; Li et al., 2024 [ ]
AcousticalRecording sound livePark et al., 2020 [ ]; Jahncke et al., 2015 [ ]; Sun et al., 2018 [ ]Environmental sound: all sounds present in the target environment were included
Hong and Jeon, 2013 [ ]; Ma and Shu, 2018 [ ]; Abdalrahman and Galbrun, 2020 [ ]; Galbrun and Calarco, 2014 [ ]; Sona et al., 2019 [ ]; Du et al., 2023 [ ]Single-resource sound: only one type of sound resource exists when recording the sound, such as water sound, bird sound, and the wind sighing in the trees
Network download soundMarcus et al., 2019 [ ]; Qi et al., 2022 [ ]
Rhythmic music Mattila and Wirtz, 2001 [ ]; Fenko and Loock, 2014 [ ]
OlfactoryFlora scent Song et al., 2019 [ ]Hinoki cypress leaf oil
Mattila and Wirtz, 2001 [ ]; Fenko and Loock, 2014 [ ]Lavender
Ba and Kang, 2019 [ ]Lilac and Osmanthus
Li et al., 2024 [ ]Coriander
Chang et al., 2023 [ ]Lavandula officinalis, Rosa rugosa, and Mentha canadensis
Qi et al., 2022 [ ]Leaves from the lawn; flowers of rose bushes; flowers of osmanthus trees; leaves (pine needles) of pine trees
Marcus et al., 2019 [ ]Grass, European silver fir, mushroom from Octanol
Wood and herb scentSona et al., 2019 [ ]A scent composed of rosewood, geranium, ylang-ylang, olibanum, and hyssop
Fruit scents Mattila and Wirtz, 2001 [ ]Grapefruit
Morrin and Chebat, 2005 [ ]Citrus
Food scentBa and Kang, 2019 [ ]Coffee and bread
Urban scentZhong et al., 2022 [ ]Natural odors, emission odors, food odors, building material odors, and human odors
Marcus et al., 2019 [ ]Diesel, tar, and gunpowder
MeasureContentReferenceRemark
Psychological measuresSensation, acceptability, pleasure, familiarity, and subjective intensityPark et al., 2020 [ ]; Hong and Jeon, 2013 [ ]; Sun et al., 2018 [ ]; Abdalrahman and Galbrun, 2020 [ ]; Galbrun and Calarco, 2014 [ ]; Aristizabal et al., 2021 [ ]; Kulve et al., 2018 [ ]; Chinazzo et al., 2019 [ ]; Ko et al., 2020 [ ]; Yang and Moon, 2019 [ ]; Yang and Moon, 2019 [ ]; Mattila and Wirtz, 2001 [ ]; Fenko and Loock, 2014 [ ]; Morrin and Chebat, 2005 [ ]; Ba and Kang, 2019 [ ]; Sona et al., 2019 [ ]; Chang et al., 2023 [ ]; Marcus et al., 2019 [ ]; Qi et al., 2022 [ ]; Zhong et al., 2022 [ ]Helped to explain participants’ attitudes toward providing sensory stimuli
PreferencesPark et al., 2020 [ ]; Hong and Jeon, 2013 [ ]; Jahncke et al., 2015 [ ]; Sun et al., 2018 [ ]; Abdalrahman and Galbrun, 2020 [ ]; Galbrun and Calarco, 2014 [ ]; Mattila and Wirtz, 2001 [ ]; Ba and Kang, 2019 [ ]; Chang et al., 2023 [ ]A straightforward way to compare different sensory combinations
Human restorationPark et al., 2020 [ ]; Jahncke et al., 2015 [ ]; Sona et al., 2019 [ ]
Emotional state Ma and Shu, 2018 [ ]; Ko et al., 2020 [ ]; Mattila and Wirtz, 2001 [ ]; Morrin and Chebat, 2005 [ ]; Sona et al., 2019 [ ]; Li et al., 2024 [ ]
PressureKo et al., 2020 [ ]; Aristizabal et al., 2021 [ ]; Marcus et al., 2019 [ ]
AnxietyFenko and Loock, 2014 [ ]; Qi et al., 2022 [ ]
Cognitive functionDesign a target search taskMa and Shu, 2018 [ ]; Aristizabal et al., 2021 [ ]Evaluated participants’ task performance
Modules of Cambridge Brain SciencesKo et al., 2020 [ ]Evaluated participants’ working memory, concentration, short-term memory, and spatial planning and used self-developed tasks to evaluate creativity performance
Psychomotor vigilance task (PVT) and spatial working memory span task (SWMS)Li et al., 2024 [ ]Evaluated cognitive performance
BiometricsFacial electromyography (fEMG)
Respiration rate (RR)
Park et al., 2020 [ ]Recorded several physiological indicators to measure the stress recovery process
Blood pressure (BP)Ma and Shu, 2018 [ ]
Heart rate (HR)Park et al., 2020 [ ]; Ma and Shu, 2018 [ ]; Aristizabal et al., 2021 [ ]; Song et al., 2019 [ ]
Electrodermal activity (EDA)Aristizabal et al., 2021 [ ]; Li et al., 2024 [ ]; Marcus et al., 2019 [ ]; Qi et al., 2022 [ ]Skin conductance level (SCL) reflects the activity of the sympathetic nervous system. Used to assess stress levels, with lower levels indicating greater relaxation
Electrocardiogram (ECG)Liu et al., 2023 [ ]; Li et al., 2024 [ ]
Electroencephalogram (EEG)Chang et al., 2023 [ ]; Li et al., 2024 [ ]; Qi et al., 2022 [ ] Analyzed changes in human mood
Employ near-infrared time-resolved spectroscopy to measure oxygen-hemoglobin concentrations in the left and right prefrontal cortex of the participantsSong et al., 2019 [ ]Investigated the physiological and psychological relaxation effects
Body/skin temperatureKulve et al., 2018 [ ]; Chinazzo et al., 2019 [ ]; Ko et al., 2020 [ ]; Qi et al., 2022 [ ]Analysis of human thermal comfort indicators
Salivary biochemical indicators: salivary stress marker (cortisol), proinflammatory cytokines, untargeted metabolomicsLi et al., 2024 [ ]
ComfortVisual comfortHong and Jeon, 2013 [ ]; Kulve et al., 2018 [ ]; Yang and Moon, 2019 [ ]; Du et al., 2023 [ ]; Zhong et al., 2022 [ ]
Acoustical comfortHong and Jeon, 2013 [ ]; Yang and Moon, 2019 [ ]; Ba and Kang, 2019 [ ]; Yang and Moon, 2019 [ ]; Du et al., 2023 [ ]; Zhong et al., 2022 [ ]
Thermal comfortKulve et al., 2018 [ ]; Ko et al., 2020 [ ]; Yang and Moon, 2019 [ ]; Chang et al., 2023 [ ]; Yang and Moon, 2019 [ ]; Du et al., 2023 [ ]
Olfactory comfortBa and Kang, 2019 [ ]; Chang et al., 2023 [ ]; Zhong et al., 2022 [ ]
Overall comfortChinazzo et al., 2019 [ ]; Yang and Moon, 2019 [ ]; Ba and Kang, 2019 [ ]; Yang and Moon, 2019 [ ]; Du et al., 2023 [ ]
Human behavior Purchasing powerMattila and Wirtz, 2001 [ ]Evaluated the extent of impulse buying in the experimental environment
Perceiver quality of productsMorrin and Chebat, 2005 [ ]
Compared patients’ perceived waiting time with the objective waiting timeFenko and Loock, 2014 [ ]
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Yin, J.; Zhu, H.; Yuan, J. Health Impacts of Biophilic Design from a Multisensory Interaction Perspective: Empirical Evidence, Research Designs, and Future Directions. Land 2024 , 13 , 1448. https://doi.org/10.3390/land13091448

Yin J, Zhu H, Yuan J. Health Impacts of Biophilic Design from a Multisensory Interaction Perspective: Empirical Evidence, Research Designs, and Future Directions. Land . 2024; 13(9):1448. https://doi.org/10.3390/land13091448

Yin, Jie, Haoyue Zhu, and Jing Yuan. 2024. "Health Impacts of Biophilic Design from a Multisensory Interaction Perspective: Empirical Evidence, Research Designs, and Future Directions" Land 13, no. 9: 1448. https://doi.org/10.3390/land13091448

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  • Systematic Review
  • Open access
  • Published: 05 September 2024

Exploring the use of social network analysis methods in process improvement within healthcare organizations: a scoping review

  • Troy Francis 1 , 2 , 3 ,
  • Morgan Davidson 1 ,
  • Laura Senese 1 ,
  • Lianne Jeffs 1 ,
  • Reza Yousefi-Nooraie 4 ,
  • Mathieu Ouimet 5 ,
  • Valeria Rac 1 , 3   na1 &
  • Patricia Trbovich 1 , 2   na1  

BMC Health Services Research volume  24 , Article number:  1030 ( 2024 ) Cite this article

Metrics details

Communication breakdowns among healthcare providers have been identified as a significant cause of preventable adverse events, including harm to patients. A large proportion of studies investigating communication in healthcare organizations lack the necessary understanding of social networks to make meaningful improvements. Process Improvement in healthcare (systematic approach of identifying, analyzing, and enhancing workflows) is needed to improve quality and patient safety. This review aimed to characterize the use of SNA methods in Process Improvement within healthcare organizations.

Relevant studies were identified through a systematic search of seven databases from inception - October 2022. No limits were placed on study design or language. The reviewers independently charted data from eligible full-text studies using a standardized data abstraction form and resolved discrepancies by consensus. The abstracted information was synthesized quantitatively and narratively.

Upon full-text review, 38 unique articles were included. Most studies were published between 2015 and 2021 (26, 68%). Studies focused primarily on physicians and nursing staff. The majority of identified studies were descriptive and cross-sectional, with 5 studies using longitudinal experimental study designs. SNA studies in healthcare focusing on process improvement spanned three themes: Organizational structure (e.g., hierarchical structures, professional boundaries, geographical dispersion, technology limitations that impact communication and collaboration), team performance (e.g., communication patterns and information flow among providers., and influential actors (e.g., key individuals or roles within healthcare teams who serve as central connectors or influencers in communication and decision-making processes).

Conclusions

SNA methods can characterize Process Improvement through mapping, quantifying, and visualizing social relations, revealing inefficiencies, which can then be targeted to develop interventions to enhance communication, foster collaboration, and improve patient safety.

Peer Review reports

Introduction

Adverse events, including medical errors, diagnostic errors, and preventable complications, continue to affect millions of patients globally, leading to severe morbidity, mortality, and substantial avoidable healthcare costs [ 1 , 2 ]. Among the many factors contributing to avoidable adverse events, breakdowns in communication have been identified as a leading cause [ 3 , 4 , 5 ]. Lapses in communication during care coordination and patient handoffs can lead to inadequate patient follow-up, delayed care, increased healthcare costs, and provider burnout, leading to an increased risk of adverse events [ 4 , 6 ].

Many studies have highlighted that investigating the underlying causes and consequences of poor communication is necessary to improve the delivery of high-quality care [ 3 , 4 , 6 , 7 ]. However, a large proportion of studies investigating communication in healthcare organizations lack the necessary understanding of social structures (interconnected relationships of social groups e.g., who speaks to who, for what purpose, using what mechanism) and coordination structures (e.g., how information gets transferred or transitioned between people or services) to make meaningful improvements and reduce adverse events [ 8 , 9 ]. For example, the surgical safety checklist (SSC) is a tool meant to enhance patient safety by coordinating care delivery and improving inter-professional communication [ 10 ]. Yet, many studies report conflicting results on the impact of the SSC due to a lack of mutual understanding of communication among team members (e.g., who is responsible for leading a specific checklist pause point) and coordination (e.g., what team members should be present during specific pause points) structures ( 11 , 12 , 13 ). Effective communication among healthcare providers is challenging due to the complex nature of tasks performed and the numerous healthcare providers embedded within hierarchical structures. While the effective use of Process Improvement or Quality Improvement (QI; framework to systematically improve processes and systems in healthcare) interventions rely on understanding the social interactions and relationships within organizations, little attention has been paid to how social networks can be used to improve the effectiveness of communication and coordination in healthcare.

A social network is a set of social entities, actors or nodes (individuals, groups, organizations) connected by similarities, social relations, interactions, or flows (information) [ 14 ]. Analyzing professional communication structures (e.g., observed formal advice-seeking or giving related to work situations) within healthcare organizations’ social networks is important in understanding how best to inform interventions by identifying which network structures promote or inhibit behavior change [ 15 ]. The use of social network analysis (SNA) can provide insight into the social relationships, interactions, and tasks involved within sociotechnical systems. SNA metrics are quantitative measures used to analyze the structure, relationships, and dynamics within social networks through quantifying network behavior [ 16 ]. Network metrics reflect centrality , which refers to a family of measures where each represent different conceptualizations of nodal importance within a network, and cohesion measures, which examine the extent to which nodes within a network are connected [ 14 , 17 ]. These metrics provide an understanding of the structure of social networks through identifying influential nodes, information flow, communities, and cliques [ 18 ]. SNA has been shown to improve professional communication and interprofessional relationships by revealing gaps in communication and identifying influential social entities and communication channels [ 14 , 15 , 19 ]. By indicating which social entities are effective in the flow of communication, organizations can leverage their skills to disseminate important information effectively and foster positive inter-professional relationships [ 19 , 20 ]. Additionally, through identifying gaps in communication between different teams or departments organizations can work to prevent misunderstandings, adverse events, and the duplication of efforts resulting in a more collaborative work environment with stronger interprofessional relationships [ 14 , 21 ]. Through understanding social networks, SNA can be effective in designing, implementing, and evaluating interventions needed to improve professional communication and coordination in healthcare [ 15 , 22 ].

The aim of this review was to characterize the existing literature to assess SNA methods ability to identify, analyze, and improve processes (Process Improvement) related to patient care within healthcare organizations.

The scoping review was conducted using Arksey and O’Malley’s modified six-step framework [ 23 , 24 ]. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) standards were used to guide the reporting of this review [ 25 ]. The PRISMA-ScR checklist is shown in the Appendix.

Information sources and search strategy

In collaboration with a research librarian (JB), relevant studies were identified through a systematic search of the MEDLINE (Ovid), Embase, Psychinfo, AMED (Allied and Complementary Medicine), CINAHL, Cochrane Library and Web of Science databases from inception – 16 October 2022. The database search was supplemented with hand searching of reference lists of included reviews. Grey literature was searched using Google Custom Search Engine strategies to narrow search results and allow for more targeted results [ 26 , 27 ]. Searched websites included the International Network for Social Network Analysis, American Evaluation Association Social Network Analysis Technical Interest Group, and the International Sunbelt Social Networks Conference proceedings archives. The search strategy for the social network analysis concept was adapted from Sabot et al.’s systematic review of Social Network Analysis and healthcare settings [ 22 ]. Truncation search terms were used to search inclusive and key terms for these concepts can be found in the supplemental appendix.

Eligibility criteria

A screening checklist developed by Sabot et al., 2017 was modified to guide the review of this study [ 22 , 28 ]. A “no” response to any of the study inclusion criteria (Appendix) was a reason for exclusion from the scoping review. “Healthcare providers” were classified as physicians, physician’s assistants, nurses, midwives, pharmacists, pharmacy technicians, clinical officers, counselors, allied health professionals, and other individuals involved in professional networks (e.g., administrative support staff, management). “Professional communication” was defined as observed formal professional advice-seeking or giving related to hypothetical or actual work situations or patients [ 22 ]. Healthcare organizations were defined as a building or mobile enclosure in which human medical, dental, psychiatric, nursing, obstetrical, or surgical care is provided. Healthcare organizations can include but are not limited to, hospitals, nursing homes, limited care facilities, medical and dental offices, and ambulatory care centers [ 29 ]. Studies had to report the use of SNA in the design of the study (e.g., social network mapping, evaluation of network properties or structure, or analysis of network actors) [ 22 ]. Additionally, to be included studies were required to use systematic data-guided activities (e.g., aims and measures) to achieve improvement or use an iterative development and testing process (i.e., Lean Management, Six Sigma, Plan-Do-Study-Act (PDSA) cycles, or Root Cause Analysis) [ 30 , 31 ]. Studies where network relations were defined solely by patient sharing were excluded, as this only predicts person-to-person communication in a minority of instances [ 32 ]. Abstracts and conference proceedings were considered if details of their methodology and results were published. No limits were placed on study design, language, or publication period.

Study selection and screening process

Study selection and screening employed an iterative process involving searching the literature, refining the search strategy, and reviewing articles for study inclusion. The titles and abstracts of all identified references were independently examined for inclusion by three reviewers (T.F, M.D, and L.S) using the Covidence software platform for systematic reviews [ 33 ]. Full texts of potentially eligible studies were retrieved by the reviewers (T.F, M.D, and L.S), who determined study eligibility using a standardized inclusion screening checklist. Inter-rater reliability was assessed at each phase of the scoping review between reviewers and disagreements were resolved by consensus with input from a fourth author (L.J).

Charting the data

Data from eligible full-text studies was charted by the reviewers (T.F, M.D, L.S) independently using a standardized data abstraction form in Covidence to obtain key items of information from the primary research reports. Discrepancies among reviewers were resolved by consensus. The data abstraction form captured information on key study characteristics (e.g., author, year of publication, location of study, study design, aim of study, type of healthcare facility/provider), SNA-related information (e.g., SNA purpose, data collection methodology, software, SNA metrics) and reported on the implications of using SNA (e.g., social network mapping, assessment of network members or structures).

Collating, summarizing, and reporting the results

A narrative synthesis was performed to describe the study characteristics, SNA methodology, and SNA metrics. The stages of the narrative synthesis included: (1) developing the preliminary synthesis, (2) comparing themes within and between studies, and (3) thematic classification [ 34 ]. Detailed text data on SNA characteristics and implications were reviewed, re-categorized, and analyzed thematically. In line with our objectives, the thematic analysis focused on identifying SNA methods used to improve communication and coordination in healthcare organizations. To categorize the approaches, we conducted further distillation of overarching approaches. We took notes throughout the review and analysis stages, documenting emerging trends and ideas to facilitate further review and discussion among the review team. The extracted data was tabulated in descriptive formats and narrative summaries were provided.

The literature search generated 5084 potentially eligible studies after deduplication, of which 4936 were excluded based on title and abstract, leaving 148 full-text articles to be reviewed. The PRISMA-ScR flow diagram outlining the breakdown of studies can be found in Fig.  1 . Upon full-text review, 44 reports of 38 studies were included for data abstraction. Six studies [ 4 , 35 , 36 , 37 , 38 , 39 ] had multiple records and were truncated into single studies.

figure 1

PRISMA-ScR flow diagram

Study characteristics

The characteristics of the included studies are shown in Table  1 . Many studies were recently published between 2015 and 2021 (26, 68%) and were primarily located in the United States (26, 68%). 67% of studies occurred within a hospital (25, 66%) and most studies (15, 39%) were set in Internal medicine (gastroenterology, oncology, cardiology, nephrology, respirology, telemetry, or acute care). Studies employed multidisciplinary healthcare providers, however many studies focused on physicians (endocrinologists, oncologists, plastic surgeons, neurologists, anesthesiologists, intensivists, generalists; 27, 71%) and nursing staff (registered nurse, nurse practitioner, practical nurse; nursing assistants; 27, 71%). Most studies employed an observational study design, with 5 studies utilizing longitudinal quasi-experimental design [ 40 , 41 , 42 , 43 , 44 ]. Five studies used mixed-methods designs [ 35 , 36 , 45 , 46 , 47 ] with integrated qualitative and quantitative data, and a further 6 studies used multi-method designs [ 48 , 49 , 50 , 51 , 52 , 53 ] using a combination of independent qualitative and quantitative data. Twenty-four studies reported using quantitative data only [ 3 , 4 , 6 , 40 , 41 , 42 , 43 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 ] and the remaining 2 studies used qualitative methods [ 71 , 72 ].

Table  2 provides an overview of the aims and findings of the included studies and Table  3 outlines the use of SNA methodology and reflects the data collection methods, software, and SNA metrics included in each study. A wide range of network visualization software was used with studies giving preferences towards UCINET [ 36 , 40 , 48 , 54 , 57 , 58 , 59 , 66 , 67 , 68 , 70 , 72 , 73 ], Organization Risk Analyzer (ORA) [ 4 , 55 , 74 , 75 ], and Open-Sourced R Software [ 42 , 49 , 53 , 63 , 65 , 76 ]. Five out of the 38 studies did not visualize their networks through social network mapping and only provided a descriptive assessment of network structures or analysis of network members [ 3 , 40 , 57 , 68 , 76 ]. Two studies did not explicitly report SNA metrics [ 47 , 61 ]. Table  4 provides a comprehensive breakdown of the SNA metrics selected in each study and their application to healthcare networks. There were many network metrics used throughout the studies, however, most studies primarily employed Degree Centrality, Betweenness Centrality, and Density. Twenty-six studies used Degree Centrality as a measure of reach and importance [ 3 , 4 , 6 , 35 , 36 , 41 , 43 , 44 , 45 , 46 , 48 , 49 , 51 , 54 , 55 , 56 , 57 , 58 , 59 , 62 , 63 , 64 , 65 , 67 , 69 , 70 ], 20 studies used Density to measure network cohesion [ 6 , 35 , 36 , 41 , 43 , 44 , 45 , 48 , 53 , 54 , 55 , 57 , 58 , 62 , 63 , 69 , 70 , 71 , 72 , 77 ], and 19 studies used Betweenness Centrality as a measure of influence and brokerage [ 3 , 4 , 36 , 44 , 45 , 46 , 49 , 51 , 52 , 55 , 56 , 57 , 59 , 60 , 62 , 63 , 65 , 66 , 69 ].

* Some articles were assigned to more than one category.

Listed in descending frequency, however “Other” is always at the bottom.

Application and findings of SNA

SNA has been used in healthcare to measure the number of connections (i.e., interactions, tasks), the centrality of providers (i.e., degree, betweenness, and closeness), and network cohesion (i.e., density, clustering). It has helped us to understand essential themes like organizational structure, team performance, and influential actors in healthcare.

a) Organizational Structure.

SNA has been used to better understand how organizational structures (e.g., management roles, groupings of tasks and employees) influence communication and coordination, thereby informing opportunities for improvement. Nine studies showed how SNA was used to redesign hospital organizational structures [ 35 , 36 , 41 , 45 , 46 , 53 , 66 , 69 , 72 ]. For example, Samarth et al. [ 69 ] applied SNA to improve the throughput of their surgical patients, which revealed a hierarchical network coordination structure in their post-anesthesia care unit (PACU) wherein the Charge Nurse channeled all communication downstream, thereby becoming a bottleneck resulting in patient delays. This led to a redesign of their organizational network to a more democratic structure where coordination was performed by an integrated information technology (IT) system which was available to all team members, reducing the dependence on the charge nurse [ 69 ]. Additionally, Alhaider et al. [ 52 ] demonstrated how SNA could be used to investigate system-wide communication in patient flow management and identify process improvement within the healthcare system. Applying SNA within the Distributed Situation Awareness (DSA) framework helped identify bottlenecks in patient flow and the roles that were most likely to experience communication or transaction overload while acquiring and disseminating situational awareness. The DSA model provided a characterization of patient flow and a blueprint for healthcare facilities to consider when modifying their organizational structure to improve communication and coordination. Spitzer-Shohat et al. [ 36 ] used SNA to understand how their organizational structure could help implement disparity reduction interventions to improve care. The SNA unveiled that their subregional management had a high degree of centrality (i.e., many connections), and as such, they were targeted to spread information about the interventions [ 36 ].

A specialized application of SNA involves identifying how IT can enhance or transform organizational communication and coordination. Three studies used SNA to understand how providers from different professions and units communicate across various modes (e.g., in-person, phone, electronic medical record) [ 4 , 48 , 69 ]. For example, SNA highlighted that IT could help improve communication efficiencies during in-person patient handoffs. More specifically, SNA showed that IT could support the redesign of the social network patterns by removing redundant communication exchanges and support emergent and non-linear information flow [ 4 , 69 ]. Six studies used electronic health records (EHR) data to map the network structure of professionals involved in care to show that improving the design of IT can support communication leading to more frequent information sharing among professional groups [ 6 , 47 , 51 , 56 , 60 , 63 ]. Nengliang et al. [ 56 ] demonstrated that EHR log data could be used within an SNA to map the network structure of all healthcare providers and examine the connectivity, centrality, and clustering of networks that emerged from interactions between providers who shared patients. In turn, this data revealed the dynamic nature of care teams and areas (inpatient and outpatient) for collaborative improvement [ 56 ]. Another study used SNA to help contrast low and high IT implementations; they found that the high IT sophistication care homes had more robust and integrated communication strategies requiring fewer face-to-face interactions between providers to verify orders or report patient status compared to the low IT sophistication nursing home [ 47 ].

b) Team Performance.

Sixteen studies used SNA to examine poor team communication and coordination by highlighting the inefficiencies in health networks [ 3 , 36 , 41 , 43 , 53 , 54 , 55 , 57 , 58 , 61 , 64 , 65 , 67 , 68 , 70 , 71 ]. SNA identified that these inefficiencies stem from: teams being overburdened due to workload [ 54 , 61 ], conflict between team roles [ 36 ], lack of leadership [ 43 , 58 ], and fragmented interprofessional relationships [ 57 , 65 , 70 ]. For example, poor team performance in hospital emergency departments has resulted in congestion and increased length of stay with patients having prolonged discharges. SNA allowed for an exploration of the possible causes of inefficiencies resulting in access blocks and determined that the number of healthcare providers and interactions between them, and the centralization of providers within the network affected the performance and quality of emergency departments [ 54 ]. Grippa et al. [ 3 ] used SNA and determined that the most efficient and effective healthcare teams focused more inwardly (internal team operation) and were less connected to external members. Additionally, SNA highlighted that effective teams communicated using only one or two mediums (e.g., in-person, email, instant messaging media) instead of dispersing time on multiple media applications.

SNA has been used to diagnose possible reasons for team inefficiencies and to identify potential design solutions to improve team performance [ 3 , 35 , 42 , 53 , 64 , 67 , 68 , 71 ]. A study used SNA to identify that some experienced staff (who frequently mentor other staff) may have too many connections (high degree of centrality), leading to interruptions or distractions and impacting performance and coordination [ 54 ]. However, a different study, identified that staff with a high degree of centrality have the benefit of improving team performance by leveraging their social networks to be change agents and lead others to replicate desired behaviors (e.g., when a provider may forget to implement a desired change but gets reminded by a team member) [ 62 ]. Lastly, analyzing network cohesion helped identify fragmentation and cliques in the network which may reflect a lack of collaboration and interprofessional relations. For instance, denser (more connections) communication networks with more clustering (groups of connections) are associated with more rapid diffusion of information. Additionally, the connections between providers in dense networks can provide social support (reinforcement) to team members that strengthen their commitment to follow desired behaviors and increase the likelihood that deviations from those actions will be noted by their peers [ 62 ].

c) Influential Actors.

SNA was used to identify influential actors who could act as brokers (an individual who occupies a specific structural position in systems of exchange) [ 3 , 49 , 64 ] who could become opinion leaders (an individual who holds significant influence over others’ attitudes/beliefs) [ 62 ], champions (an individual who actively supports innovation and its promotion/implementation) [ 40 ] or a change agent (an early adopter of an intervention who supports the dissemination of its use) [ 44 ] based off measures of social influence within a network. Studies showed that influential actors in social networks can inform behavioral interventions needed to improve professional communication or coordination [ 3 , 40 , 49 , 62 , 64 ]. For example, Meltzer et al. [ 62 ] used SNA to identify influential physicians to join a QI team and highlighted that having members with connections external to the team is most important when disseminating information, while within team relationships matter most when coordination, knowledge sharing, and within-group communication are most important. When creating an interdisciplinary team, betweenness centrality (node that frequently lies on the shortest path in a network) may be a useful network metric for prospectively identifying team members that may help to facilitate coordination within and across units / professional groups. Providers with a high betweenness have been found to be leaders and active participants in task-related groups [ 68 ]. Hurtado et al. [ 40 ] used SNA to identify and recruit champions who were used to deploy a QI intervention (safe patient handling education program) to advance safety in critical access hospitals. The champion-centered approach resulted in improved safety outcomes (increase in safety participation/compliance and decrease in patient-assist injuries) after one year. Additionally, Lee et al. [ 44 ] used SNA to assess the use of peer-identified and management-selected change agents on improving hand hygiene behavior in acute healthcare. No significant differences were reported between the two groups; however providers expressed a preference for hierarchical leadership styles highlighting the need to understand organizational culture before designing changes to the system.

This scoping review presents a comprehensive overview of the existing literature looking at the use and impact of SNA methodology on Process Improvement within healthcare organizations. Our search strategy included a wide range of databases and placed no restrictions on study design, language, or publication period. When examining the expanding body of literature represented in our identified 38 studies, SNA methods were used to detect essential work processes in organizations, reveal bottlenecks in workflow, offer insight into resource allocation, evaluate team performance, identify influential providers, and monitor the effectiveness of process improvements over time. By analyzing the communication and relationships between management roles, employee groupings, and task allocation, SNA provides insights that can help identify areas for improvement related to patient throughput, diffusion of information, and the uptake of technology (e.g., IT systems). Studies highlighted that healthcare team performance can be hampered by inefficiencies related to being overburdened due to workload, conflicts between team roles, lack of leadership, and fragmented interprofessional relationships. To address these inefficiencies, SNA can leverage network outcomes related to connectedness (e.g., degree, betweenness, closeness) and use knowledge of the network structure (e.g., density, clustering coefficient, fragmentation) to create targeted interventions to mitigate these problems. Additionally, inefficiencies in social networks can be mitigated by identifying influential actors who serve as change agents and can be utilized as opinion leaders or champions to improve the efficiency of information exchange and the uptake of behavioral interventions.

Comparison With Past Literature (Study Design and Data Collection).

Our review stands out from previous studies due to its unique focus on the application of SNA methods in Process Improvement within healthcare organizations. Our primary objective was to investigate how healthcare organizations utilize SNA techniques to improve system-level coordination and enhance the overall quality of care provided to patients. In their research study, Sabot et al. [ 22 ] aimed to investigate the various SNA methods employed to examine professional communication and performance among healthcare professionals. Their study delved into the diverse range of SNA techniques used to gain insights into the complex network dynamics and interactions among providers. In more recent studies, Saatchi et al. [ 78 ] focused on exploring the adoption and implementation of network interventions in healthcare settings. This study provided insights into the effectiveness of network interventions (in which contexts they are successful and for whom), their potential benefits (increased volume of communication), and the challenges associated with their adoption in practice. Additionally, Rostami et al. [ 79 ] focused on advancing quantitative SNA techniques and investigated the application of community detection algorithms in healthcare. This study offers a comprehensive categorization of SNA community detection algorithms and explores potential approaches to overcome gaps and challenges in their use. Previous reviews primarily included observational and cross-sectional study designs with no comparator arms, which made determining the value of using SNA methods difficult as there was no comparison of social networks over time and no comparable head-to-head data. Our review identified 5 quasi-experimental studies [ 40 , 41 , 42 , 43 , 44 ] which used longitudinal or pre-post study designs. In each of these studies SNA was used to review a system which delivered clinical care to identify sources of variation and areas for process improvement at an individual and organizational level. The quasi-experimental studies were published within the last 5 years, indicating that SNA methodology is still in development and opportunities for experimental and longitudinal study designs are forthcoming. Using experimental and longitudinal SNA methods would enable causal inference of healthcare interventions or policies leading to improved generalizability of results.

When performing SNA there is a variety of qualitative (interviews, focus groups, observations) and quantitative (surveys, document artifacts, information systems) methods that researchers can use to map social networks, assess network structures, and analyze team actors. However, previous literature reviews have outlined an overreliance on descriptive SNA methods, which lack the contextual factors needed to interpret how a network reached a given structure. There has been a growing body of evidence advocating for the use of mixed-method social network data collection [ 80 ]. Our review has highlighted an increased uptake of mixed-method (integration of qualitative and quantitative methods and data) and multi-method (independent use of quantitative and qualitative methods) SNA study designs [ 81 ].

Knowledge Gaps and Future Research.

This scoping review highlights many practical uses of SNA; however, within most studies, little attention has been paid to leveraging SNA theory to help explain why networks have the structures they do [ 21 ]. For example, social boundaries between professional groups (e.g., Physicians, Nurses, Pharmacists) can inhibit the development of interprofessional networks though the creation of cliques leading to strong communication and coordination within groups, but fragmented communication across professional groups [ 21 , 82 , 83 ]. A potential explanation for the scarcity of studies assessing the reasons behind the structures of networks could be attributed to the primarily quantitative SNA methods used. Few studies used a qualitative or mixed-method design, indicating a limited understanding of the contextual factors associated with social networks. SNA can reveal the informal structures within organizations and underscores the importance of understanding that not all influential relationships between healthcare providers are found on formal organizational charts, and that informal networks can significantly influence communication and coordination [ 84 ]. The lack of robust study designs (mixed-method or multi-method) may also reflect the use of SNA by researchers more so as a technique than a methodology with theoretical underpinnings.

The value of using SNA to inform research and disseminate evidence-based interventions and policies has been discussed in the literature extensively. However, very few studies have used research on complex systems and network theory to examine how HCWs can act as change agents, interacting within and between hubs in organizations to disseminate knowledge [ 85 ]. Future research should apply complexity science to SNA to reconceptualize knowledge translation and think of the process as interdependent and relationship-centric to support sustainable translation [ 85 ]. Only a small group of included articles have highlighted how leveraging influential actors as change agents such as opinion leaders or champions can be advantageous in improving professional communication or coordination [ 3 , 40 , 44 , 49 , 62 , 64 ]. This review identified two studies [ 40 , 44 ] which utilized SNA and a champion-centered approach to support the successful implementation of a QI intervention resulting in improved safety outcomes. The use of champions is very prevalent in healthcare; however, success rates vary widely, likely due to the poor selection of champion candidates or organizational culture [ 40 , 44 ]. In many cases healthcare workers selected to be champions are volunteered and do not hold enough social influence to change the behaviors of their colleagues. In the future SNA methods should be used to identify influential champions or opinion leaders embedded within their social networks who can influence knowledge transfer and facilitate coordination leading to process improvements.

Future research should identify how SNA methods can leverage health informatics and the large amounts of data stored within healthcare organizations. Even though past studies have used SNA to enhance organizational communication and coordination using IT [ 47 , 56 , 69 ], applying SNA to artificial intelligence and machine learning (ML) algorithms has not received much attention [ 86 ]. Integrating ML algorithms into community detection techniques has showcased the diverse ways SNA can be utilized in healthcare to monitor disease diagnosis, track outbreaks, and analyze HCW networks [ 79 ].

Limitations of the Review.

This review has some limitations that should be acknowledged. First, we excluded studies of provider friendship networks, which theoretically may have contained some professional communication. Secondly, we excluded studies where network relations were defined solely by patient sharing, as this has only been shown to predict person-to-person communication in a minority of instances. Lastly, studies were required to incorporate a Process Improvement component. Different terms were used to describe Process Improvement in the literature, making it challenging to devise a search strategy that would yield sufficient articles for review while also utilizing SNA methods. As a result, studies that utilized SNA methods but did not explicitly examine a process or system for delivering clinical care to identify sources of variation and areas for improvement were excluded.

SNA methods can be used to characterize Process Improvements through mapping, quantifying, and visualizing social relations revealing inefficiencies, which can then be targeted to develop interventions to enhance communication, foster collaboration, and improve patient safety. However, healthcare organizations still lack an understanding of the benefit of using SNA methods to reduce adverse events due to a lack of experimental studies. By emphasizing the importance of understanding professional communication and coordination within healthcare teams, units, and organizations, our review underscores the relationship between organizational structures and the potential of influential actors and emerging IT technologies to mitigate adverse events and improve patient safety.

Data availability

All data generated or analyzed during this study are included in this published article [and its supplementary information files].

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Acknowledgements

The authors would like to thank Joanna Bielecki for her assistance in developing the search strategy and Sonia Pinkney for her valuable feedback and suggestions in refining this manuscript.

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Valeria Rac and Patricia Trbovich contributed equally to this work.

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Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada

Troy Francis, Morgan Davidson, Laura Senese, Lianne Jeffs, Valeria Rac & Patricia Trbovich

HumanEra, Research and Innovation, North York General Hospital, Toronto, ON, Canada

Troy Francis & Patricia Trbovich

Program for Health System and Technology Evaluation, Toronto General Hospital Research Institute, University Health Network, Toronto, ON, Canada

Troy Francis & Valeria Rac

Department of Public Health Sciences, University of Rochester, New York, USA

Reza Yousefi-Nooraie

Department of Political Science, Université Laval, Quebec, Canada

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experimental design research methodology

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  • Published: 05 September 2024

Multi-objective optimization of an EDM process for Monel K-500 alloy using response surface methodology-multi-objective dragonfly algorithm

  • Prosun Mandal 1 ,
  • Suman Mondal 2 ,
  • Robert Cep 3 &
  • Ranjan Kumar Ghadai 4  

Scientific Reports volume  14 , Article number:  20757 ( 2024 ) Cite this article

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  • Engineering
  • Materials science
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Monel K-500 is a high-performance superalloy composed of nickel and copper, renowned for its exceptional strength, hardness, and resistance to corrosion. To machine this material more precisely and accurately, Electrical Discharge Machining (EDM) is one of the best choices. In EDM, material removal rate (MRR) and electrode wear rate (EWR) are crucial performance parameters that are often conflicting in nature. These parameters depend on several input variables, including peak current (Ip), pulse on time (Ton), duty cycle (Tau), and servo voltage (SV). Optimizing the EDM process is essential for enhancing performance. In this research, a set of experiments were conducted using EDM on Monel K500 alloy to determine the optimal process parameters. The Box–Behnken design was used to prepare the experimental design matrix. Utilizing the experimental data, a second-order mathematical model was developed using Response Surface Methodology (RSM). R 2 value is found to be 99.40% and 96.60% for MRR and EWR RSM-based prediction model, respectively. High value of R 2 is indicated is indicated good adequacy for prediction. The mathematical model further used in multi-objective dragonfly algorithm (MODA): a new meta-heuristic optimization technique to solve multi-objective optimization problem of EDM. The MODA is a very useful technique to achieve optimal solutions from the multi decision criteria. Utilizing this technique, a set of non-dominated solutions was obtained. Further, the TOPSIS method was used to determine the most desirable optimal solution, which was found to be 0.0135 mm 3 /min for EWR and 6.968 mm 3 /min for MRR. These results were obtained when the optimal process parameters were selected as Ip = 6 A, Ton = 200 µs, Tau = 12, and SV = 41.6 V. Operators can machine Monel K500 by selecting the above-mentioned optimal parameters to achieve the best performance.

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Introduction.

Currently, manufacturing industries face the challenge of machining various alloy or composite materials with high strength, hardness, and temperature resistance. Unconventional machining processes are employed to handle such difficult-to-cut materials, ensuring high surface finish, precise dimensional accuracy, and intricate shapes. 1 . Electro-discharge machining (EDM) employs the thermal energy of sparks to remove material. It finds application in the machining of hardened steel dies, aerospace, automotive, and machine tool components, as well as in the production of medical components 2 , 3 . The extensive use of EDM in manufacturing, particularly for machining newly developed advanced materials, renders it a significant subject of research. Numerous researchers have delved into the EDM process while machining various materials. Ahmed et al. 4 investigate the EDM process with the aim of minimizing geometrical errors, surface roughness, and tool wear in machined titanium alloy components. Asif et al. 5 found that machining efficiency is a crucial indicator for sustainable EDM machining. To improve efficiency, eco-friendly Tween series surfactants were added to the dielectric fluid while machining Ti6Al4V ELI alloy and investigated the effects of various process parameters on performance. The material removal rates (MRR) and tool wear rates (TWR) of EDM are crucial performance parameters 6 , 7 , 8 . Farooq et al. 9 identified and investigated the influence of process parameters, namely pulse current, pulse on time, pulse off time, polarity, and dielectric, on EDM performance during the machining of titanium alloy. Various researchers observed that different process parameters have diverse effects on multiple performance parameters. Nguyen et al. 10 observed a significant impact of peak current on machinability, noting that crater size depends on spark energy. Balasubramanian et al. 11 found that peak current is the principal influencing parameter for MRR and surface roughness during the machining of high manganese steel. During machining titanium alloy, the pulse on time emerges as a predominant factor 12 . Izwan et al. 13 utilized four different materials: brass, aluminum, high-strength steel, and high-strength low-alloy steel. It is found that higher peak current and longer pulse-on time resulted in an increased Material Removal Rate (MRR). Tran et al. 14 optimized the machining process of AISI P20 steel using Taguchi and ANOVA analyses. It is highlighted that current significantly impacts Material Removal Rate (MRR), Electrode Wear Rate (EWR), and Surface Roughness (SR). The surface roughness found to be decrease with increases in pulse on time, pulse off time, and current. Hussain et al. 15 assessed that peak current is the primary determinant factor that affecting on MRR and EWR during the machining of aluminum oxide-copper composite, by employing the Taguchi method. Researchers have established that different EDM performance parameters are influenced by different process parameters such as pulse-on time, pulse-off time, peak current, and voltage.

The performance parameters in EDM often conflict, with different process variables impacting various outcomes in diverse ways. Therefore, optimally selecting these parameters is crucial for enhancing EDM performance. To achieve this, a range of modeling and optimization techniques have been extensively employed to identify the most suitable machining parameters, thereby improving overall performance 16 , 17 , 18 . To enhance the sustainability of the EDM process, Sana et al. 19 used alumina-mixed deionized water as the dielectric fluid. Additionally, the EDM process was modeled using artificial neural networks (ANN) and optimized it with non-dominated sorting genetic algorithms (NSGA-II). Machine learning based predictive model for EDM process found to be an effective way to enhancing the performance 20 , 21 . Kaigude et al. 22 employed machine learning methods, including linear regression, decision trees, and random forests, to predict the surface roughness during the machining of AISI D2 steel in the presence of Titanium dioxide (TiO2) nanopowder in the dielectric. Seidi et al. 23 applied methods based on the removal effects of criteria (MEREC) and the weighted aggregates sum product assessment (WASPAS) techniques to address multi-objective optimization in the wire electrical discharge machining process. Sing et al. 24 employed Meta-heuristic optimization techniques, including Teaching Learning-Based Optimization (TLBO) and Particle Swarm Optimization (PSO) algorithms, for electro-discharge machining of 316L porous stainless steel. Mandal and Mondal 25 used MOPSO-TOPSIS to solve the multi objective optimization problem of EDM. Bhowmick et al. 26 developed a prediction model for Material Removal Rate (MRR) and surface roughness in titanium-mixed Electrical Discharge Machining (EDM) of Inconel 718 using Response Surface Methodology (RSM) and fuzzy logic, optimizing the process parameters. RSM encompasses a set of mathematical and statistical techniques valuable for modeling and analyzing problems where a response of interest is affected by multiple variables, with the aim of optimizing these responses 27 . Joshi et al. 28 compared multi-objective optimization techniques, including the non-dominated sorting genetic algorithm II (NSGA-II), multi-objective ant lion optimization (MOALO), and multi-objective dragonfly optimization (MODA), in micro-turning and micro-milling. Chang et al. 29 employed the NSGA-II algorithm to solve a multi-objective optimization problem. Wang et al. 30 utilized MODA analysis to develop a hybrid forecasting framework in electrical power systems. While these meta-heuristic techniques have effectively addressed optimization problems, their application in solving multi-objective optimization problems in EDM operations is rare.

Monel K-500, a nickel-based superalloy, exhibits exceptional corrosion resistance, as well as high strength and toughness across a broad temperature range 31 .

Machining nickel-based alloys such as Monel K-500 poses a challenge for many traditional machining processes due to their inherent limitations. EDM is a correct alternative solution for machining of Monel materials. In a study conducted by Akgün 32 , machining of Monel K-500 superalloy using Electrical Discharge Machining (EDM) was investigated with various electrodes. The results indicate that the copper electrode outperforms the graphite electrode for machining Monel K-500 alloy. Though the nickel-based alloy Monel K-500 has huge applicability and EDM is an effective way for machining, very few research works are found on experimental investigation and optimization of the EDM process during machining of Monel K500 material. Therefore, a number of experiments were conducted adopting RSM Box-Behnken design of experiment on Monel K-500 alloy. Mathematical models were developed using RSM for MRR and EWR. Further, the RSM models were used as objective function in dragonfly algorithm: a new meta-heuristic optimization technique to solve the multi objective optimization problem.

The extensive literature survey has highlighted that the nickel-based alloy Monel K-500 is difficult to machine using traditional machining processes. However, non-traditional methods, such as Electrical Discharge Machining (EDM), present a viable alternative. It was also found that different process parameters have varying effects on performance parameters, with many performance parameters exhibiting conflicting behaviors. Modeling and optimization are essential techniques for enhancing EDM performance. Therefore, in this current work, EDM operations were performed on Monel K-500 alloy to solve a multi-objective optimization problem. To determine the optimal EDM process parameters, Response Surface Methodology (RSM) and a newly developed Multi-Objective Dragonfly Algorithm (MODA) were employed.

Materials and methods

After conducting a comprehensive review of the existing literature on the parametric optimization of Electrical Discharge Machining (EDM) parameters for various materials and alloys, MONEL K-500 alloy was selected as the workpiece material for experimentation. Tables 1 and 2 provide the chemical composition and physical properties of the MONEL K-500 alloy, respectively. As shown in Table 2 , the mechanical properties of MONEL K-500, such as yield strength, ultimate tensile strength, and hardness, are relatively high, making it challenging to machine using traditional methods. However, its high electrical conductivity makes it suitable for EDM processes.

A flat rectangular plate with dimensions of (116 × 75) mm and a thickness of 5 mm was used for the experiments. The experiments were conducted following the Box–Behnken design of Response Surface Methodology.

Experimental setup

The flowchart illustrating the current research is shown in Fig.  1 . The experiments were conducted using a die-sinking EDM machine (Model ELTECH D-300ZNC, India) at the IIEST, Shibpur, India, as illustrated in Fig.  2 . Since the workpiece material is non-magnetic, the plate was secured in place by clamping it with mild steel plates, which are magnetic, as depicted in Fig.  3 . Blind holes with a depth of 0.5 mm were created for each set of parameters. To calculate the material removal rate (MRR) and electrode wear rate (EWR), the time taken during each machine run was carefully monitored using a stopwatch and recorded. The weight before and after machining each specimen was measured using a precision weighing machine with a least count of 0.001g.

figure 1

Flowchart of research.

figure 2

EDM experimental set-up.

figure 3

Pre-machining setup.

Experimental array

The experimental array is formed by combining input process variables to determine the conditions under which the experiments are conducted. This array is influenced by different process variables and their respective settings. In this particular study, four process variables—peak current (Ip), pulse on time (Ton), duty cycle (Tau), and servo voltage (SV)—are employed for experimental purposes. These parameters significantly affect the Material Removal Rate (MRR) and Electrode Wear Rate (EWR). In EDM, optimizing these parameters is crucial for achieving the desired balance between MRR and EWR. While higher peak currents, pulse-on times, and duty cycles increase MRR, they also tend to increase EWR. Conversely, higher servo voltages decrease both MRR and EWR by widening the spark gap and reducing discharge intensity. Therefore, finding an optimal set of parameters is essential for efficient and effective machining, ensuring high MRR while minimizing electrode wear. The range of input machining variables is detailed in Table 3 . The selection of process variables, their ranges, and levels is based on the experimental data set provided with EDM.

In the current research, a Box–Behnken-based experimental array is employed within an identified search space (n = 1). The initial investigation aimed to confine the input process variables within the operational range. Following the determination of this range, the experimental design was executed, as outlined in Table 4 . All experiments were conducted according to the run order rather than a conventional sequence. This approach aligns with the principle of randomness, ensuring the reproducibility of machine tool results. A total of 27 experiments were carried out, with each experiment being replicated twice to uphold the statistical precision of the results.

Response surface methodology

Mathematical modelling using Response Surface Methodology (RSM) 33 , 34 involves developing mathematical equations to represent the relationship between input factors (independent variables) and a response (dependent variable). The primary goal is to create a predictive model that can guide experimentation and optimization of the system.

Here are the key steps in mathematical modelling using RSM:

Experimental design:

Conduct a well-planned experimental design, varying the input factors at different levels. Use a factorial design or fractional factorial design to efficiently explore the factor space.

Data collection:

Collect data on the response variable at each combination of factor levels.

Ensure that the data collection is accurate and representative of the system under study.

Fit a mathematical model:

Choose a suitable mathematical model based on the nature of the relationship between factors and response. Common models include linear, quadratic, and cubic equations.

The general quadratic model can be represented as:

where: Y is the predicted response, \({b}_{0}, {b}_{i}, {b}_{ii }and {b}_{ij}\) are coefficients to be determined, \({X}_{i}\) represents the levels of the independent variables, \(\epsilon \) is the error term.

Parameter estimation:

Use statistical methods such as least squares estimation to determine the coefficients in the model.

Model validation:

Validate the model by comparing predicted responses with actual experimental data not used in the model fitting. Statistical techniques such as analysis of variance (ANOVA) are often employed for model validation.

Multi-Objective Dragonfly Algorithm (MODA)

The Dragonfly Algorithm (DA) is a nature-inspired optimization algorithm based on the swarming behaviour of dragonflies. It is a meta-heuristic optimization technique that simulates the social interactions and foraging behaviour of dragonfly swarms to solve optimization problems. Mirjalili 35 introduced the MODA, an optimization algorithm founded on swarm intelligence, in 2014. Here's an overview of the Dragonfly Optimization Algorithm:

Swarming Behaviour:

The algorithm is inspired by the collective behaviour of dragonflies in nature, where they exhibit coordinated movements and group hunting for efficient prey capture.

Search Agents (Dragonflies):

Dragonflies in the algorithm represent the search agents. Each dragonfly corresponds to a potential solution in the search space.

Objective Function:

The optimization problem is defined by an objective function that needs to be either minimized or maximized.

Movement and Interaction:

Dragonflies move within the search space based on their current positions and the positions of other dragonflies. This movement is influenced by social interactions.

Prey Capture and Exploration:

Dragonflies engage in prey capture behaviour, focusing on regions with promising solutions. Exploration and exploitation are balanced to avoid premature convergence.

Algorithm Steps:

Initialization:

Initialize a population of dragonflies with random positions in the search space.

Evaluation:

Evaluate the objective function for each dragonfly to determine their fitness.

Update the position of each dragonfly based on its current position, the positions of other dragonflies, and predefined movement rules.

Prey Capture:

Dragonflies adjust their positions to focus on areas with better solutions, mimicking the prey capture behaviour in nature.

Update Best Solution:

Update the global best solution if a dragonfly discovers a better solution than the current best.

Termination:

Repeat the movement and prey capture steps iteratively until a stopping criterion is met (e.g., a maximum number of iterations or achieving a satisfactory solution).

The Dragonfly Algorithm has been applied to various optimization problems, including engineering design, scheduling, and parameter optimization in machine learning.

Results and discussion

The regression model employing Response Surface Methodology (RSM) has been established to predict Material Removal Rate (MRR) and Electrode Wear Rate (EWR). This model is formulated as a function of peak current (Ip), pulse on time (Ton), duty cycle (Tau), and servo voltage (SV), utilizing experimental data. The adequacy of the developed quadratic models was evaluated through Analysis of Variance (ANOVA). The significance of both the overall model and individual model terms was determined using F-tests and P-tests.

Influence of process parameters on MRR

ANOVA is utilized to assess the significance and percentage contribution of all elements in the model. Backward elimination is applied to eliminate insignificant terms without influence on the model, and the model's adequacy is tested at each step. The terms with p values less than 0.05 are considered significant. Table 4 shows the ANOVA and fit summary of MRR during machining of Monel K500 using EDM. Linear term SV, square term Ton × Ton, Tau × Tau and 2-Way Interaction term Ip × SV, Ton × SV and Tau × SV are found to be insignificant as p-value greater than 0.05 and this term can be removed from the model using backward elimination. Table 5 shows the \({R}^{2}\) value for the model. \({R}^{2}\) is an important statistical parameter which defines the variability in responses. Higher value of \({R}^{2}\) shows the good correlation between the response values and experimental values. Moreover, \({R}^{2}\) increases while adding terms to the model. It does not predict whether the added terms are significant or insignificant. Thus, the fitness of the regression model cannot be explained by a larger \({R}^{2}\) . Therefore, another statistical parameter namely adjusted \({R}^{2}\) ( \({R}^{2}\) -adj) is used which decreases by the inclusion of insignificant terms to the model. The \({\text{R}}^{2}\) value is found to be 99.40% which implies the high relational factor between variables and factors.

Figure  4 displays four distinct plots: a normal probability plot illustrating the relationship between residuals and percent, versus fit plots portraying the relationship between fitted values and residuals, a histogram depicting the frequency distribution of residuals, and order plots illustrating the relationship between observation order and residuals. These plots are presented for MRR. In Fig.  3 , it is observed that the residual values, representing the differences between experimental and mathematically predicted values, closely align with the normal probability line. This observation suggests that the errors are distributed in a normal manner, indicating that the models are suitable for prediction. The residuals for the MRR prediction model range from -5 to 5. Lower values within these ranges indicate higher accuracy in the RSM prediction models. In Fig.  3 , a notable concentration of frequency is observed around the zero value, indicating minimal error in mathematical modelling within the RSM model. The graphical representation of residuals (the difference between experimental and mathematically predicted values) versus observed values is shown in Fig.  3 . The residuals appear randomly scattered around zero across various observed values, indicating a well-fitted RSM model for prediction.

figure 4

Residual plots of RSM model for MRR.

Percentage contribution (PC) of terms are depicted in same ANOVA table (Table 4 ). It is found that in linear part, Ip is the dominating EDM parameter with PC of 86.16 followed by Ton and T au are 5.9 and 5.73, respectively. Spark current (Ip) has highest influence on MRR. High current supply means high energy supply to the sparking zone which causes higher amount of material remove from machining zone. The empirical quadratic mathematical model, expressed in coded units for MRR as a function of peak current (Ip), pulse on time (Ton), duty cycle (Tau), and servo voltage (SV), is presented in Eq. ( 2 ).

Influence of process parameters on EWR

A full quadratic model, similar to the MRR analysis, also investigates for EWR of EDM operation. ANOVA table (Table 6 ) shows that linear term Tau and SV, square terms, Ton × Ton, Tau × Tau and SV × SV, and two-way interaction term Ip × Tau, Ip × SV, Ton × SV and Tau × SV are found to be insignificant. Linear term Ip has highest percentage of contribution with 61.51% on EWR and it is followed by another linear term Ton with percentage of contribution of 26.57%. The \({\text{R}}^{2}\) value for the EWR model is found to be 96.60% which implies the high adequacy for prediction of EWR. Residual plot (Fig.  5 ) for EWR is supporting evidence for the adequacy of the predicted model. From the residual plots, it is noticed that p value calculated based on Anderson–Darling (AD) statistic test is greater than the significance level of 0.05. This indicates that the residuals are normally distributed, and it can be inferred that the developed quadratic model for EWR is adequate. The residuals for the EWR prediction model range from − 0.05 to 0.05. Lower values within these ranges indicate higher accuracy in the RSM prediction models. The histogram plot depicting the frequency distribution of residuals. From the plot, it is observed that residual is concentrated on very close to zero. All these evidence are indicated a very high adequacy of EWR model. The empirical quadratic mathematical model, expressed in coded units for EWR as a function of peak current (Ip), pulse on time (Ton), duty cycle (Tau), and servo voltage (SV), is presented in Eq. ( 3 ).

figure 5

Residual plots of RSM model for EWR.

Multi-objective optimization using MODA

The key EDM responses, EWR and MRR, exhibit conflicting characteristics.

The important EDM response EWR and MRR are conflicting in nature. Different process parameters have different percentages of contribution on EWR and MRR. Therefore, it is crucial to identify the optimal combination of input parameters to achieve reduced EWR and increased MRR. Below are two objective functions provided:

In this research, MODA was utilized for multi-objective optimization under parameter constraints. The fitness functions in MODA (MATLAB 2015a) are based on a second-order mathematical model for EWR "(1)" and MRR "(2)". The population size, or number of search agents, is maintained at 100. Equal weightage is assigned to each fitness function. To minimize EWR and maximize MRR, specific boundary conditions should be adhered to selecting the EDM process parameters, namely peak current (Ip), pulse on time (Ton), duty cycle (Tau), and servo voltage (SV). The boundary conditions for the process parameters are outlined as follows:

The concept of Pareto dominance was utilized to identify a set of non-dominated solutions 36 , 37 . Figure  6 illustrates the Pareto-optimal frontier, showing the distribution of points generated from the response optimization. Each point on the curve represents an optimal solution, giving users the flexibility to choose any point to conduct experiment. The non-dominated solutions (Pareto front) obtained from the MODA outputs were employed in the TOPSIS method to determine the most desirable solution. Equal importance was provided to each of the objectives. The best optimal solution was derived by executing the TOPSIS methodology. The point, highlighted on the Pareto frontiers (Fig.  6 ), signifies the optimal point selected through the TOPSIS technique. Table 7 presents the optimal values of the objective functions and their corresponding optimal decision parameters, obtained through the MODA-TOPSIS technique.

figure 6

Pareto-optimal frontier chart.

Experimental confirmation of optimal results

The confirmation test was performed with the MODA-TOPSIS predicted optimal input parameter setting (Table 7 ). The experimental results were compared with the predicted ones. The findings from the confirmation test and error percentages are shown in Table 8 . It was observed that the error percentages for EWR and MRR stand at 6.67% and 2.54%, respectively. The validation of the MODA prediction model was confirmed by the lower error percentages observed between predicted and experimental values in EDM operation. Thus, it can be inferred that the experimental results validate the efficacy of the MODA-TOPSIS technique, making it a reliable method for predicting optimal process parameters in EDM operation.

This study focused on the Electrical Discharge Machining (EDM) processes applied to Monel K-500 Alloy by exploring various process parameters. An experimental design matrix was prepared using a Box-Behnken-based experimental array. The experiments were conducted according to this design matrix, and the resulting experimental dataset was used to develop a second-order polynomial regression model. The adequacy of this model was confirmed through ANOVA analysis, which demonstrated its high accuracy in predicting both the Material Removal Rate (MRR) and the Electrode Wear Rate (EWR).

The optimization of EDM process parameters was performed using the Multi-Objective Dragonfly Algorithm (MODA), relying on fitness functions to identify optimal solutions. In this optimization problem, EWR and MRR were treated as objective functions, with EWR being minimized and MRR maximized. Non-dominated optimal solutions for EWR and MRR were obtained, ranging from (0.0135, 6.968) to (0.0317, 6.649) along the Pareto optimal frontier. The Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) was employed to select the most desirable optimal solution, assigning equal importance to each objective function. The optimal results for EWR and MRR in the EDM operation were found to be 0.0135 mm 3 /min and 6.968 mm 3 /min, respectively. These results were achieved with the following specific process parameters: pulse current (Ip) of 6 amps, pulse-on time (Ton) of 200 µs, duty cycle (Tau) of 12, and servo voltage (SV) of 41.6 V. The outcomes obtained through the MODA-TOPSIS method were validated with a confirmation test, demonstrating satisfactory performance.

Selecting these optimal process parameters can enhance the quality and efficiency of EDM processes involving Monel K-500. Although this study did not investigate the microstructure and surface integrity during EDM, this presents a promising area for future research.

Data availability

The data presented in this study are available in the article.

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Acknowledgements

This article was co-funded by the European Union under the REFRESH-Research Excellence For REgion Sustainability and High-tech Industries project number CZ.10.03.01/00/22_003/0000048 via the Operational Programme Just Transition and has been done in connection with project Students Grant Competition SP2024/087 “Specific Research of Sustainable Manufacturing Technologies” financed by the Ministry of Education, Youth and Sports and Faculty of Mechanical Engineering VŠB-TUO.

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Mandal, P., Mondal, S., Cep, R. et al. Multi-objective optimization of an EDM process for Monel K-500 alloy using response surface methodology-multi-objective dragonfly algorithm. Sci Rep 14 , 20757 (2024). https://doi.org/10.1038/s41598-024-71697-5

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