medical research types

• Skip to main content
• Skip to FDA Search
• Skip to in this section menu
• Skip to footer links

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you're on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

U.S. Food and Drug Administration

•   Search
•   Menu
• For Patients
• Clinical Trials: What Patients Need to Know

What Are the Different Types of Clinical Research?

Different types of clinical research are used depending on what the researchers are studying. Below are descriptions of some different kinds of clinical research.

Treatment Research generally involves an intervention such as medication, psychotherapy, new devices, or new approaches to surgery or radiation therapy. 

Prevention Research looks for better ways to prevent disorders from developing or returning. Different kinds of prevention research may study medicines, vitamins, vaccines, minerals, or lifestyle changes. 

Diagnostic Research refers to the practice of looking for better ways to identify a particular disorder or condition. 

Screening Research aims to find the best ways to detect certain disorders or health conditions. 

Quality of Life Research explores ways to improve comfort and the quality of life for individuals with a chronic illness. 

Genetic studies aim to improve the prediction of disorders by identifying and understanding how genes and illnesses may be related. Research in this area may explore ways in which a person’s genes make him or her more or less likely to develop a disorder. This may lead to development of tailor-made treatments based on a patient’s genetic make-up. 

Epidemiological studies seek to identify the patterns, causes, and control of disorders in groups of people. 

An important note: some clinical research is “outpatient,” meaning that participants do not stay overnight at the hospital. Some is “inpatient,” meaning that participants will need to stay for at least one night in the hospital or research center. Be sure to ask the researchers what their study requires. 

Phases of clinical trials: when clinical research is used to evaluate medications and devices Clinical trials are a kind of clinical research designed to evaluate and test new interventions such as psychotherapy or medications. Clinical trials are often conducted in four phases. The trials at each phase have a different purpose and help scientists answer different questions. 

Phase I trials Researchers test an experimental drug or treatment in a small group of people for the first time. The researchers evaluate the treatment’s safety, determine a safe dosage range, and identify side effects. 

Phase II trials The experimental drug or treatment is given to a larger group of people to see if it is effective and to further evaluate its safety.

Phase III trials The experimental study drug or treatment is given to large groups of people. Researchers confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the experimental drug or treatment to be used safely. 

Phase IV trials Post-marketing studies, which are conducted after a treatment is approved for use by the FDA, provide additional information including the treatment or drug’s risks, benefits, and best use.

Examples of other kinds of clinical research Many people believe that all clinical research involves testing of new medications or devices. This is not true, however. Some studies do not involve testing medications and a person’s regular medications may not need to be changed. Healthy volunteers are also needed so that researchers can compare their results to results of people with the illness being studied. Some examples of other kinds of research include the following: 

A long-term study that involves psychological tests or brain scans

A genetic study that involves blood tests but no changes in medication

A study of family history that involves talking to family members to learn about people’s medical needs and history.

Research Types Explained: Basic, Clinical, Translational

“Research” is a broad stroke of a word, the verbal equivalent of painting a wall instead of a masterpiece. There are important distinctions among the three principal types of medical research — basic, clinical and translational.

Whereas basic research is looking at questions related to how nature works, translational research aims to take what’s learned in basic research and apply that in the development of solutions to medical problems. Clinical research, then, takes those solutions and studies them in clinical trials. Together, they form a continuous research loop that transforms ideas into action in the form of new treatments and tests, and advances cutting-edge developments from the lab bench to the patient’s bedside and back again.

Basic Research

When it comes to science, the “basic” in basic research describes something that’s an essential starting point. “If you think of it in terms of construction, you can’t put up a beautiful, elegant house without first putting in a foundation,” says David Frank, MD , Associate Professor of Medicine, Medical Oncology, at Dana-Farber Cancer Institute. “In science, if you don’t first understand the basic research, then you can’t move on to advanced applications.”

Basic medical research is usually conducted by scientists with a PhD in such fields as biology and chemistry, among many others. They study the core building blocks of life — DNA, cells, proteins, molecules, etc. — to answer fundamental questions about their structures and how they work.

For example, oncologists now know that mutations in DNA enable the unchecked growth of cells in cancer. A scientist conducting basic research might ask: How does DNA work in a healthy cell? How do mutations occur? Where along the DNA sequence do mutations happen? And why?

“Basic research is fundamentally curiosity-driven research,” says Milka Kostic, Program Director, Chemical Biology at Dana-Farber Cancer Institute. “Think of that moment when an apple fell on Isaac Newton’s head. He thought to himself, ‘Why did that happen?’ and then went on to try to find the answer. That’s basic research.”

Clinical Research

Clinical research explores whether new treatments, medications and diagnostic techniques are safe and effective in patients. Physicians administer these to patients in rigorously controlled clinical trials, so that they can accurately and precisely monitor patients’ progress and evaluate the treatment’s efficacy, or measurable benefit.

“In clinical research, we’re trying to define the best treatment for a patient with a given condition,” Frank says. “We’re asking such questions as: Will this new treatment extend the life of a patient with a given type of cancer? Could this supportive medication diminish nausea, diarrhea or other side effects? Could this diagnostic test help physicians detect cancer earlier or distinguish between fast- and slow-growing cancers?”

Successful clinical researchers must draw on not only their medical training but also their knowledge of such areas as statistics, controls and regulatory compliance.

Translational Research

It’s neither practical nor safe to transition directly from studying individual cells to testing on patients. Translational research provides that crucial pivot point. It bridges the gap between basic and clinical research by bringing together a number of specialists to refine and advance the application of a discovery. “Biomedical science is so complex, and there’s so much knowledge available.” Frank says. “It’s through collaboration that advances are made.”

For example, let’s say a basic researcher has identified a gene that looks like a promising candidate for targeted therapy. Translational researchers would then evaluate thousands, if not millions, of potential compounds for the ideal combination that could be developed into a medicine to achieve the desired effect. They’d refine and test the compound on intermediate models, in laboratory and animal models. Then they would analyze those test results to determine proper dosage, side effects and other safety considerations before moving to first-in-human clinical trials. It’s the complex interplay of chemistry, biology, oncology, biostatistics, genomics, pharmacology and other specialties that makes such a translational study a success.

Collaboration and technology have been the twin drivers of recent quantum leaps in the quality and quantity of translational research. “Now, using modern molecular techniques,” Frank says, “we can learn so much from a tissue sample from a patient that we couldn’t before.”

Translational research provides a crucial pivot point after clinical trials as well. Investigators explore how the trial’s resulting treatment or guidelines can be implemented by physicians in their practice. And the clinical outcomes might also motivate basic researchers to reevaluate their original assumptions.

“Translational research is a two-way street,” Kostic says. “There is always conversation flowing in both directions. It’s a loop, a continuous cycle, with one research result inspiring another.”

Learn more about research at Dana-Farber .

Masks Strongly Recommended but Not Required in Maryland

Respiratory viruses continue to circulate in Maryland, so masking remains strongly recommended when you visit Johns Hopkins Medicine clinical locations in Maryland. To protect your loved one, please do not visit if you are sick or have a COVID-19 positive test result. Get more resources on masking and COVID-19 precautions .

• Vaccines  
• Masking Guidelines
• Visitor Guidelines  

Understanding Clinical Trials

Clinical research: what is it.

Your doctor may have said that you are eligible for a clinical trial, or you may have seen an ad for a clinical research study. What is clinical research, and is it right for you?

Clinical research is the comprehensive study of the safety and effectiveness of the most promising advances in patient care. Clinical research is different than laboratory research. It involves people who volunteer to help us better understand medicine and health. Lab research generally does not involve people — although it helps us learn which new ideas may help people.

Every drug, device, tool, diagnostic test, technique and technology used in medicine today was once tested in volunteers who took part in clinical research studies.

At Johns Hopkins Medicine, we believe that clinical research is key to improve care for people in our community and around the world. Once you understand more about clinical research, you may appreciate why it’s important to participate — for yourself and the community.

What Are the Types of Clinical Research?

There are two main kinds of clinical research:

Observational Studies

Observational studies are studies that aim to identify and analyze patterns in medical data or in biological samples, such as tissue or blood provided by study participants.

Clinical Trials

Clinical trials, which are also called interventional studies, test the safety and effectiveness of medical interventions — such as medications, procedures and tools — in living people.

Clinical research studies need people of every age, health status, race, gender, ethnicity and cultural background to participate. This will increase the chances that scientists and clinicians will develop treatments and procedures that are likely to be safe and work well in all people. Potential volunteers are carefully screened to ensure that they meet all of the requirements for any study before they begin. Most of the reasons people are not included in studies is because of concerns about safety.

Both healthy people and those with diagnosed medical conditions can take part in clinical research. Participation is always completely voluntary, and participants can leave a study at any time for any reason.

“The only way medical advancements can be made is if people volunteer to participate in clinical research. The research participant is just as necessary as the researcher in this partnership to advance health care.” Liz Martinez, Johns Hopkins Medicine Research Participant Advocate

Types of Research Studies

Within the two main kinds of clinical research, there are many types of studies. They vary based on the study goals, participants and other factors.

Biospecimen studies

Healthy volunteer studies.

 Goals of Clinical Trials

Because every clinical trial is designed to answer one or more medical questions, different trials have different goals. Those goals include:

Treatment trials

Prevention trials, screening trials, phases of a clinical trial.

In general, a new drug needs to go through a series of four types of clinical trials. This helps researchers show that the medication is safe and effective. As a study moves through each phase, researchers learn more about a medication, including its risks and benefits.

Is the medication safe and what is the right dose?   Phase one trials involve small numbers of participants, often normal volunteers.

Does the new medication work and what are the side effects?   Phase two trials test the treatment or procedure on a larger number of participants. These participants usually have the condition or disease that the treatment is intended to remedy.

Is the new medication more effective than existing treatments?  Phase three trials have even more people enrolled. Some may get a placebo (a substance that has no medical effect) or an already approved treatment, so that the new medication can be compared to that treatment.

Is the new medication effective and safe over the long term?   Phase four happens after the treatment or procedure has been approved. Information about patients who are receiving the treatment is gathered and studied to see if any new information is seen when given to a large number of patients.

“Johns Hopkins has a comprehensive system overseeing research that is audited by the FDA and the Association for Accreditation of Human Research Protection Programs to make certain all research participants voluntarily agreed to join a study and their safety was maximized.” Gail Daumit, M.D., M.H.S., Vice Dean for Clinical Investigation, Johns Hopkins University School of Medicine

Is It Safe to Participate in Clinical Research?

There are several steps in place to protect volunteers who take part in clinical research studies. Clinical Research is regulated by the federal government. In addition, the institutional review board (IRB) and Human Subjects Research Protection Program at each study location have many safeguards built in to each study to protect the safety and privacy of participants.

Clinical researchers are required by law to follow the safety rules outlined by each study's protocol. A protocol is a detailed plan of what researchers will do in during the study.

In the U.S., every study site's IRB — which is made up of both medical experts and members of the general public — must approve all clinical research. IRB members also review plans for all clinical studies. And, they make sure that research participants are protected from as much risk as possible.

Earning Your Trust

This was not always the case. Many people of color are wary of joining clinical research because of previous poor treatment of underrepresented minorities throughout the U.S. This includes medical research performed on enslaved people without their consent, or not giving treatment to Black men who participated in the Tuskegee Study of Untreated Syphilis in the Negro Male. Since the 1970s, numerous regulations have been in place to protect the rights of study participants.

Many clinical research studies are also supervised by a data and safety monitoring committee. This is a group made up of experts in the area being studied. These biomedical professionals regularly monitor clinical studies as they progress. If they discover or suspect any problems with a study, they immediately stop the trial. In addition, Johns Hopkins Medicine’s Research Participant Advocacy Group focuses on improving the experience of people who participate in clinical research.

Clinical research participants with concerns about anything related to the study they are taking part in should contact Johns Hopkins Medicine’s IRB or our Research Participant Advocacy Group .

Learn More About Clinical Research at Johns Hopkins Medicine

For information about clinical trial opportunities at Johns Hopkins Medicine, visit our trials site.

Video Clinical Research for a Healthier Tomorrow: A Family Shares Their Story

Clinical Research for a Healthier Tomorrow: A Family Shares Their Story

Types of Primary Medical Research

Medical research may be classified as either primary or secondary research. Primary research entails conducting studies and collecting raw data. Secondary research evaluates or synthesizes data collected during primary research.

Primary medical research is categorized into three main fields: laboratorial, clinical, and epidemiological. Laboratory scientists analyze the fundamentals of diseases and treatments. Clinical researchers collaborate with participants to test new and established forms of treatment. Epidemiologists focus on populations to identify the cause and distribution of diseases.

Basic/Laboratory Research

Laboratory, or basic, research involves scientific investigation and experimentation in a controlled environment to establish or confirm an understanding of chemical interactions, genetic material, cells, and biologic agents—more specifically, the agent’s relationships, behaviors, or properties. Basic science forms the knowledge-base and foundation upon which other types of research are built. Laboratory scientists investigate specific hypotheses which contribute to the development of new medical treatments.

An advantage of this type of research is that scientists can control the variables within a laboratory setting. Such a high level of control is often not possible outside of the laboratory. This leads to greater internal validity of a hypothesis and allows the testing of various aspects of disease and potential treatments. The key to laboratory research is to establish at least one independent variable, while holding all others constant. The standardized conditions of a laboratory setting also support the development of new medical imaging and diagnostic tools.

Applied research aims to solve problems such as treating a particular disease that is under investigation. There a number of different study types within applied research, including:

• Animal studies: Animals are often induced to have a particular disease model so that the disease and potential treatments can be better understood for use with humans.
• Biochemistry: Focuses upon the chemical processes that occur within the body; biochemistry also explores the metabolic basis of disease.
• Cell study: Examines how cells develop and each cell type’s potential role in disease or treatment.
• Genomics: Explores how all genes interact to influence the growth, health, and potential disease development of an organism/human.
• Pharmacogenetics: Pharmacogenetics seeks to better understand the influence genes have upon how a patient might respond to any treatments they may receive. 3

Theoretical

Clinical Research

Clinical research is conducted to improve the understanding, treatment, or prevention of disease. Clinical studies examine individuals within a selected patient population. This type of research is usually interventional, but may also be observational or preventional. In order to categorize clinical research, it is useful to look at two factors: 1) the timing of the data collection (whether the study is retrospective or prospective) and 2) the study design (e.g. case-control, cohort). 4 Study integrity is improved through randomization, blinding, and statistical analysis. Researchers often test the efficacy and safety of drugs in clinical drug studies. Many clinical trials have a pharmacological basis. In addition, clinical studies may examine surgical, physical, or psychological procedures as well as new or conventional uses for medical devices. Researchers may perform diagnostic, retrospective, or case series observational studies to diagnose, treat, and monitor patients.

Treatments, dosages, and population can be exactly specified to control or minimize internal differences aside from the treatment.

Interventional/Clinical Trials

Clinical trials are defined by phases, with the first phase (Phase I) being the introduction of a new drug in to the human population. Before Phase I, animal testing will have been undertaken. 5 Phase I is conducted to assess the safety and maximum dosage that a majority or a significant portion of patients are able to tolerate. The following list describes the key elements of each clinical trial phase . 7

• Phase I: This is the initial step in any drug development, a Phase I clinical trial includes a small number of people (usually 20-100) to determine the safety of a drug and the appropriate dosage.
• Phase II: After success at Phase I, Phase II trials include larger groups of individuals (~100-300) and work to determine both efficacy as well as potential adverse reactions.
• Phase III: At this stage, larger numbers of individuals (~300-3,000) with a specific condition are included within the trial. Trials seek to establish intervention effectiveness in treating a condition under normal use and to establish more robust safety and side effect data.
• Phase IV: Following approval for public use, Phase IV trials are undertaken to understand the long-term impact of an intervention. At this stage, the drug may also be tested on “at-risk” populations, such as the elderly, to make sure that it is safe for a broader population.

Observational

In observational studies, the researcher does not seek to control any variables. Instead, the researcher observes participants (often retrospectively) over a specified period of time. In contrast to controlled and randomized interventional studies, treatment decisions are left to the doctor and patient. Comparisons may be made between individuals given two different types of therapy or having different prognostic variables (e.g. a particular condition). Diagnostic studies evaluate the accuracy of a diagnostic test or method in predicting or identifying a specific condition. Once a number of studies have undertaken an analysis of a single variable, a secondary analysis can take place either via a meta-analysis or literature review in order to see if there is consistency across study results.

Epidemiological Research

Epidemiologists investigate the causes, distribution, and historical changes in the frequency of disease. For example, researchers have looked for trends in cancer or flu outbreaks to determine their cause and ways to prevent or reduce the spread either of these types of disease. These studies can be interventional, but are usually observational due to ethical, social, political, and health risk factors.

Interventional

• Intervention Study: These studies explore changes in health or disease outcomes after the introduction of a specific intervention. For example, the effect of adding fluoride to drinking water was studied through interventional epidemiologic studies in the United States in the 1940s. Another study undertaken in the U.S. sought to assess how a diet high in fruit and vegetables and low in red meat and processed food might impact sodium levels of individuals when compared with a traditional American diet. 6
• Cohort (Follow-up) Study: Observational studies can include many thousands of individuals and because of this, they can be time-consuming and expensive to undertake. To overcome some of these costs, researchers may choose to focus upon a particular group of people (known as a cohort) and explore the health of this group in relation to specific variables. For example, studies have sought to understand how different levels of exercise improve health outcomes.
• Case control: Particularly useful when seeking to explore rare diseases because the population with the disease has already been identified. The group of individuals identified with the disease is then compared to individuals without the disease with the purpose of exploring how the health outcomes differ between the two groups.
• Cross-sectional: Used to explore the levels of disease within a population (prevalence). Cross-sectional studies provide a snapshot of what is happening within a particular population at one period of time.
• Ecological: Tend to analyze data from previously published sources in order to explore the health of populations and the potential causes of ill health.
• Monitoring/Surveillance: Many countries record and survey populations in order to fully understand the health of their populations.
• Description with registry data: In the United States, cancer registries collect data about the numbers of cases of site-specific cancers each year. This information can then be used to explore rates of cancer at a local level to examine whether incidence and prevalence are changing over time.
• Röhrig, B., du Prel, J.-B., Wachtlin, D. & Blettner, M. Types of study in medical research: part 3 of a series on evaluation of scientific publications. Dtsch Arztebl Int 106, 262–268 (2009).
• Haidich, A. B. Meta-analysis in medical research. Hippokratia 14, 29–37 (2010).
• Ma, Q. & Lu, A. Y. H. Pharmacogenetics, pharmacogenomics, and individualized medicine. Pharmacol. Rev. 63, 437–459 (2011).
• Sessler, D. I. & Imrey, P. B. Clinical Research Methodology 1: Study Designs and Methodologic Sources of Error. Anesth. Analg. 121, 1034–1042 (2015).
• Umscheid, C. A., Margolis, D. J. & Grossman, C. E. Key concepts of clinical trials: a narrative review. Postgrad Med 123, 194–204 (2011).
• Svetkey, L. P. et al. The DASH Diet, Sodium Intake and Blood Pressure Trial (DASH-Sodium). Journal of the American Dietetic Association 99, S96–S104 (1999).
• U.S. Food & Drug Administration. The Drug Development Process.

Contributors

Vanessa Gordon-Dseugo, MPH, PhD; Grace Satterfield, MS

Published: January 17, 2019 Revised: September 2, 2020

• Fundamental Skills Education Improvement Leadership Research
• Additional Skills Communication Entrepreneur Finance Self Development
• Careers Training Pathways Out of Training Alternative Careers

Scroll to the bottom of the webpage to ensure images load completely before printing.

Types of Study

Introduction to Types of Medical Research

Evidence-based medicine may be defined as the systematic, quantitative and preferentially experimental approach to obtaining medical information. This information is obtained through medical research. Medical research encompasses a wide range of study techniques that can be used to understand diseases, uncover their causative factors and validate the treatments we have available for them. Each type of study technique comes with advantages as well as their own particular disadvantages. This article will introduce the different types of study commonly used within medical research and discuss their particular traits. The diagram below provides an overview of how the different types of study methodology relate to one another.

Primary vs. Secondary Research

Medical research can be classified as either primary or secondary research. Primary research involves performing studies and collecting raw data. Secondary research involves evaluating or synthesising data collected during primary research.

Observational vs. Experimental Research

An observational study is a study in which the investigator does not seek to control any of the variables nor the assignment of intervention to subjects. These decisions are usually made by the patient and their doctor. Examples include cohort, case-control, case-series and cross-sectional studies.

An experimental study involves direct manipulation or assignment of participants to different interventions or environments. Clinical experimental studies are known as clinical trials.

Prospective vs. Retrospective

In prospective studies , individuals are followed over a period of time and data is collected when their characteristics or circumstances change. Studies usually relate the outcome of interest to suspected risk factors. For these prospective studies, the outcome of interest should commonly occur to ensure statistical significance. Prospective studies allow precise estimation of the relative risk of an outcome based upon exposure.

In retrospective studies , individuals are sampled and information is collected about their past. These studies usually establish an outcome of interest and examine exposures to suspected risk or protective factors. Data is typically gathered from interviews or medical notes. The nature of retrospective studies makes them more susceptible to bias. Retrospective studies allow calculation of the odds ratio (this is an estimate of the relative risk) for uncommon outcomes. Retrospective studies are advantageous for studying rare diseases since prospective studies are unfeasible due to the large study sizes needed to reach statistical significance.

Randomised vs. Non-Randomised

Randomised studies involve the random allocation of individuals to intervention groups in order to minimise confounding variables. Allocation does not take into account any similarities or differences in the individuals. It usually involves use of a random number generator.

Non-randomised studies involve allocation of people to different interventions using methods which are not random.

Single-Blinded vs. Double Blinded vs. Triple-Blinded

Blinding is important to reduce bias and ensure a study’s internal validity. It prevents participants and researchers from affecting the outcomes of a study in a conscious or subconscious manner.

• Single-blind study – only the participants are blinded.
• Double-blind study – both participants and experimenters are blinded.
• Triple-blind study – participants, experimenters and researchers analysing the data are blinded.

The Levels of Evidence

Not all evidence is created equal with some forms of study technique thought to be superior in design. Studies which employ superior designs are felt to carry more weight when interpreting their conclusions. The result is the creation of a hierarchy based upon study technique. This has been outlined in the diagram below.

The ordering of evidence in this manner may be seen as simplistic because it does not take into account the methodological merit of individual study designs. Furthermore, the quality of systematic review evidence will depend largely upon the type of study included within the analysis and meta-analysis results can vary wildly depending upon the statistical methods employed. In the final instance, systematic reviews should be considered a lens through which evidence can be viewed.

Brief Description of Study Types

In this section we will cover the basics of the following study designs.

• Meta-Analysis
• Systematic Review
• Randomised Control Trial
• Cohort Study
• Case Control Series
• Case Report/Series

For further information on each of these study designs and how to perform them, have a look at the Equator Network .

Meta-Analysis - Secondary Research

Definition: A meta-analysis is a statistical procedure for systematically combining numerical (quantitative) data from multiple independent studies in the published literature. These data are assessed and used to derive conclusions about that body of research. It is a subset of systematic reviews (see below).

Uses: Meta-analyses can be used to provide more precise estimates than those given by any individual study included within the analysis. They may also answer questions not posed by individual studies or identify and examine the heterogeneity between the individual studies (including statistical significance where conflicting results are reported). Examples of alternative questions include providing a more complex analysis of harms/benefits or the examination of subgroups where individual study numbers were not large enough.

Brief Methodology: The Cochrane collaboration has developed a protocol which provides structure for literature search, analytic and diagnostic methods for evaluating the output of meta-analyses. These can be viewed within their handbook . Additional guidance can be found by using PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). This is an evidence-based minimum set of items (checklist) for reporting in systematic reviews and meta-analyses.

• Provides greater statistical power and increased volume of data for more precise estimates.
• Hypothesis testing and biases within publications can be examined.
• Inconsistencies within research can be resolved.
• Provides better estimate of relationships.

Disadvantages

• It is difficult and time consuming to identify the correct studies.
• Not all studies may be appropriate for inclusion.
• An incomplete set of studies may have been analysed.
• Requires advanced statistical capabilities.
• Heterogeneity of methods used in studies may lead to erroneous inferences.

Systematic Review - Secondary Research

Definition: A systematic review is a detailed, systematic and transparent means of considering all published and unpublished material which fits within a prespecified eligibility criteria. The included material can be of varying study designs. Those materials which are judged to be methodologically sound are combined in either a quantitative or qualitative manner to answer a pre-defined research question. Meta-analyses are not required but many systematic reviews will include a meta-analysis.

Uses: Systematic reviews are used to deliver a meticulous summary of the available primary research in response to a research question.

Brief Methodology: Systematic reviews should have a clear set of objectives, predefined eligibility criteria, a reproducible methodology, a systemic search method, an assessment of the validity of the findings of included studies and a systematic presentation and synthesis of the attributes and findings from the studies used.

• Addresses a specific question.
• Explicit and bias limiting methods.
• More reliable and accurate than individual studies.
• Less costly than organising a new study.
• Requires less time than a new study.
• Results can be generalised and extrapolated into the general population.
• Time consuming.
• There may be difficulties combining different studies.
• May be composed of inadequate primary studies.
• May be poorly designed and executed.
• May mis-interpret results.

Randomised Controlled Trial - Primary Research, Experimental, Prospective

Definition: A randomised control trial involves one or more new treatments where participants are randomly assigned into an experimental or control group. The various groups are then followed up to see if there is any difference in the specified outcome. The results and subsequent analysis are used to evaluating the effectiveness of the intervention.

Uses: Randomised controlled trials are used to establish the effectiveness of a new intervention or treatment.

Brief Methodology: Interventions might include a medication or procedure. Control groups will either get a placebo treatment or receive the current ‘gold standard’ treatment. Randomisation seeks to evenly distribute baseline characteristics in order to reduce the effect of confounding variables. This process is usually performed using mathematical techniques.

The CONSORT (Consolidated Standards of Reporting Trials) Statement can be used as an evidence-based minimum set of recommendations (checklist) for reporting randomised trials. The Cochrane Library has formed a highly concentrated source of reports of randomised controlled trials which can be found within their CENTRAL (Cochrane Central Register of Controlled Trials) database.

• You can make direct comparisons between treatments.
• Effective randomisation removes selection bias.
• Randomisation reduces the impact of confounding factors and makes groups comparable with both known and unknown factors.
• Results can be reliably analysed with statistical tools.
• Blinding can be applied to reduce performance bias.
• Prospective design minimises recall error and selection bias.
• It is expensive and takes time.
• Participants must volunteer and so may not be representative of the whole population.
• Studies will have to be powered sufficiently to make significant outcomes.
• There is the risk of participants being lost to follow up.
• Ethical limitations. For example, informed consent is impossible to obtain, or some intervention arms would be ethically impossible.
• Results may not mimic realise and generalisability to the real world may be difficult.

Cohort Studies - Primary Research, Observational, Predominantly Prospective

Definition: Groups of disease-free individuals are identified, and baseline measurements are taken for a variety of variables (risk factors) that might be relevant to the development of the outcome of interest. These individuals are then followed over time to determine whether they develop the outcome of interest. Cohort studies are usually prospective but can be performed retrospectively with data collected for other purposes.

Uses: Cohort studies measure incidence rates and the relative risk for developing the outcome of interest for each measured variable. They are able to distinguish between cause and effect due to the temporal relationship between risk factor exposure and outcome occurrence.

Brief Methodology: In prospective cohort studies the risk exposure information is collected at the start of the study and new cases of disease identified from that point onwards. In retrospective cohort studies the exposure status was measured in the past and disease identification has already begun. Both methods enable calculation of the relative risk.

The STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) statement (checklist) can be used to ensure observational studies are adequately described in research publications. This checklist has been designed for cohort studies, case-control studies and cross-sectional studies.

• It is cheaper and easier to implement than a randomised controlled trial.
• It is able to distinguish between cause and effect.
• Multiple outcomes can be studied.
• It may uncover unanticipated associations with the outcome.
• The efficiency of prospective cohort studies increases as the incidence of any particular outcome increases.
• Patients can be lost to follow up thereby introducing attrition bias.
• Subject selection can introduce bias due to an imbalance of patient characteristics.
• It is prone to change of methods over time.
• Confounding variables can be difficult to remove.
• It is difficult to blind researchers.
• Requires large numbers of patients.
• The outcome of interest can take a long time to occur.

Case Control Studies - Primary Research, Observational, Retrospective

Definition: A study that compares patients who have an outcome of interest (the disease in question) with those who do not. Case control studies are almost always retrospective. The researcher looks back in time to identify which individuals were exposed to a risk factor or treatment and thus the relation it has with the presence or absence of disease.

Uses: Good for studying rare diseases and outcomes. They can also be used where there is a long latent period between an exposure and disease occurrence. They are often used to generate hypotheses that can then be studied using other means.

Brief Methodology: Individuals with the outcome of interest (the disease in question) are selected (cases). A second group of similar individuals without the outcome of interest is constructed (controls). The researcher then looks at historical factors to identify if some exposures are found more commonly in the cases than the controls. If this is the case, a link can be established between the exposure and the outcome of interest. This produces an odds ratio that can be used to approximate the relative risk for each variable studied.

Case Report/Series - Primary Research, Observational, Retrospective

Definition: An article that describes and interprets an individual case or cases. It is often written as a detailed story.

Brief Methodology: An interesting case is identified, and the patient should be described in detail. Include the following: their age, sex, ethnicity, race, employment status, social situation, medical history, diagnosis, prognosis, previous treatments, diagnostic tests, medications, current intervention and the clinical and functional assessment.

Uses: Describe unique cases that cannot be explained by known diseases or syndromes. They may show an important variation from a known disease. They may show unexpected events that yield new information. They may include patients with two or more unexpected diseases or disorders.

• Stats Direct
• Cochrane Handbook
• CONSORT Statement: Cosolidated Standards of Reporting Trials
• PRISMA Statement: Preferred Reporting Items for Systematic Reviews and Meta-Analyses
• STROBE Statement: Strengthening the Reporting of Observational Studies in Epidemiology
• Equator Network: Enhancing the Quality and Transparency of Health Research
• Open MD: Medical Research
• Deutsches Ärzteblatt International: Types of Study in Medical Research
• Himmelfarb: Types of Studies
• Georgia State University: Literature Reviews: Types of Clinical Study Designs
• Deutsches Ärzteblatt International: Systematic Literature Reviews and Meta-Analyses
• Emergency Medicine Journal: Randomised Controlled Trials and Their Principles

Also in Research

Writing your First Research Article

The Anatomy of a Research Article

P-Values and Confidence Intervals

Introduction to Descriptive Statistics

Introduction to Inferential Statistics

Diagnostic Tables

Relative Risk and Odds Ratio

Data Visualisation

• Remote Access
• Save figures into PowerPoint
• Download tables as PDFs

Chapter 3:  Types of Studies in Clinical Research—Part I: Observational Studies

• Download Chapter PDF

Disclaimer: These citations have been automatically generated based on the information we have and it may not be 100% accurate. Please consult the latest official manual style if you have any questions regarding the format accuracy.

Download citation file:

• Search Book

Jump to a Section

Introduction, research design and studies.

• STUDIES OF RISK ASSESSMENT: OBSERVATIONAL STUDIES
• Full Chapter
• Supplementary Content

When you have completed this chapter, you will be able to understand:

Types of studies and their relation to the research objectives

The different types of studies

The difference between primary and secondary studies

The different types of primary studies

Descriptive and analytical observational studies

Various descriptive observational studies and their functions

Various analytical observational studies and their functions

The advantages and disadvantages of observational studies

The previous chapter described the various steps of planning and conducting a research study. This chapter briefly introduces the reader to the different types of studies and then elaborates on the observational studies. In observational studies, the researcher observes the involvement of the participants and collects data by simply observing events as they happen, without playing an active part in what takes place. In interventional, or experimental, studies, the investigator exposes the participants to some kind of intervention and tries to find a relation between the intervention and the outcome. Observational studies can be descriptive, like the case studies and case series, but are more commonly analytical (cross-sectional, case–control, and cohort studies). Descriptive observational studies describe characteristics of a population and usually do not have a hypothesis; they are sometimes hypothesis-generating studies. An analytical observational study, in addition, tries to find a causal relationship between two or more comparable groups (variables) and has a hypothesis to prove.

A study design is a road map or blueprint based on the type of research to be carried out. It starts with development of the research question, formulating a hypothesis and research objectives, and subsequent planning for carrying out the research. The research objectives of the proposed study determine the type of study to be undertaken.

Types of Studies

Type of studies in medical research can be broadly classified into primary and secondary studies. Primary studies are those that are actually performed by the investigators, while secondary studies summarize the results of different primary studies in the form of systematic reviews and meta-analyses without actually performing the studies. 1 Primary studies can be put into three groups based on the type of research undertaken: basic medical or experimental studies, epidemiologic studies, and clinical studies. Basic medical studies include research in animal experiments, cell studies, biochemical, genetic and physiologic investigations, and studies on the properties of drugs and materials. Epidemiologic studies investigate the distribution and historical changes in the frequency of diseases and the causes for these diseases, while clinical studies involve research in human subjects. However, it may be difficult to classify individual studies into one of these three main categories. 1 A more practical way to classify the types of research studies based on their function is to group them into observational and interventional (experimental) studies; the former can be further subclassified into descriptive and analytical studies ( Figure 3-1 ).

Get Free Access Through Your Institution

Pop-up div successfully displayed.

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.

Please Wait

• U.S. Department of Health & Human Services

• Virtual Tour
• Staff Directory
• En Español

You are here

Nih clinical research trials and you.

The NIH Clinical Trials and You website is a resource for people who want to learn more about clinical trials. By expanding the below questions, you can read answers to common questions about taking part in a clinical trial. 

What are clinical trials and why do people participate?

Clinical research is medical research that involves people like you. When you volunteer to take part in clinical research, you help doctors and researchers learn more about disease and improve health care for people in the future. Clinical research includes all research that involves people.  Types of clinical research include:

• Epidemiology, which improves the understanding of a disease by studying patterns, causes, and effects of health and disease in specific groups.
• Behavioral, which improves the understanding of human behavior and how it relates to health and disease.
• Health services, which looks at how people access health care providers and health care services, how much care costs, and what happens to patients as a result of this care.
• Clinical trials, which evaluate the effects of an intervention on health outcomes.

What are clinical trials and why would I want to take part?

Clinical trials are part of clinical research and at the heart of all medical advances. Clinical trials look at new ways to prevent, detect, or treat disease. Clinical trials can study:

• New drugs or new combinations of drugs
• New ways of doing surgery
• New medical devices
• New ways to use existing treatments
• New ways to change behaviors to improve health
• New ways to improve the quality of life for people with acute or chronic illnesses.

The goal of clinical trials is to determine if these treatment, prevention, and behavior approaches are safe and effective. People take part in clinical trials for many reasons. Healthy volunteers say they take part to help others and to contribute to moving science forward. People with an illness or disease also take part to help others, but also to possibly receive the newest treatment and to have added (or extra) care and attention from the clinical trial staff. Clinical trials offer hope for many people and a chance to help researchers find better treatments for others in the future

Why is diversity and inclusion important in clinical trials?

People may experience the same disease differently. It’s essential that clinical trials include people with a variety of lived experiences and living conditions, as well as characteristics like race and ethnicity, age, sex, and sexual orientation, so that all communities benefit from scientific advances.

See Diversity & Inclusion in Clinical Trials for more information.

How does the research process work?

The idea for a clinical trial often starts in the lab. After researchers test new treatments or procedures in the lab and in animals, the most promising treatments are moved into clinical trials. As new treatments move through a series of steps called phases, more information is gained about the treatment, its risks, and its effectiveness.

What are clinical trial protocols?

Clinical trials follow a plan known as a protocol. The protocol is carefully designed to balance the potential benefits and risks to participants, and answer specific research questions. A protocol describes the following:

• The goal of the study
• Who is eligible to take part in the trial
• Protections against risks to participants
• Details about tests, procedures, and treatments
• How long the trial is expected to last
• What information will be gathered

A clinical trial is led by a principal investigator (PI). Members of the research team regularly monitor the participants’ health to determine the study’s safety and effectiveness.

What is an Institutional Review Board?

Most, but not all, clinical trials in the United States are approved and monitored by an Institutional Review Board (IRB) to ensure that the risks are reduced and are outweighed by potential benefits. IRBs are committees that are responsible for reviewing research in order to protect the rights and safety of people who take part in research, both before the research starts and as it proceeds. You should ask the sponsor or research coordinator whether the research you are thinking about joining was reviewed by an IRB.

What is a clinical trial sponsor?

Clinical trial sponsors may be people, institutions, companies, government agencies, or other organizations that are responsible for initiating, managing or financing the clinical trial, but do not conduct the research.

What is informed consent?

Informed consent is the process of providing you with key information about a research study before you decide whether to accept the offer to take part. The process of informed consent continues throughout the study. To help you decide whether to take part, members of the research team explain the details of the study. If you do not understand English, a translator or interpreter may be provided. The research team provides an informed consent document that includes details about the study, such as its purpose, how long it’s expected to last, tests or procedures that will be done as part of the research, and who to contact for further information. The informed consent document also explains risks and potential benefits. You can then decide whether to sign the document. Taking part in a clinical trial is voluntary and you can leave the study at any time.

What are the types of clinical trials?

There are different types of clinical trials.

• Prevention trials look for better ways to prevent a disease in people who have never had the disease or to prevent the disease from returning. Approaches may include medicines, vaccines, or lifestyle changes.
• Screening trials test new ways for detecting diseases or health conditions.
• Diagnostic trials study or compare tests or procedures for diagnosing a particular disease or condition.
• Treatment trials test new treatments, new combinations of drugs, or new approaches to surgery or radiation therapy.
• Behavioral trials evaluate or compare ways to promote behavioral changes designed to improve health.
• Quality of life trials (or supportive care trials) explore and measure ways to improve the comfort and quality of life of people with conditions or illnesses.

What are the phases of clinical trials?

Clinical trials are conducted in a series of steps called “phases.” Each phase has a different purpose and helps researchers answer different questions.

• Phase I trials : Researchers test a drug or treatment in a small group of people (20–80) for the first time. The purpose is to study the drug or treatment to learn about safety and identify side effects.
• Phase II trials : The new drug or treatment is given to a larger group of people (100–300) to determine its effectiveness and to further study its safety.
• Phase III trials : The new drug or treatment is given to large groups of people (1,000–3,000) to confirm its effectiveness, monitor side effects, compare it with standard or similar treatments, and collect information that will allow the new drug or treatment to be used safely.
• Phase IV trials : After a drug is approved by the FDA and made available to the public, researchers track its safety in the general population, seeking more information about a drug or treatment’s benefits, and optimal use.

What do the terms placebo, randomization, and blinded mean in clinical trials?

In clinical trials that compare a new product or therapy with another that already exists, researchers try to determine if the new one is as good, or better than, the existing one. In some studies, you may be assigned to receive a placebo (an inactive product that resembles the test product, but without its treatment value).

Comparing a new product with a placebo can be the fastest and most reliable way to show the new product’s effectiveness. However, placebos are not used if you would be put at risk — particularly in the study of treatments for serious illnesses — by not having effective therapy. You will be told if placebos are used in the study before entering a trial.

Randomization is the process by which treatments are assigned to participants by chance rather than by choice. This is done to avoid any bias in assigning volunteers to get one treatment or another. The effects of each treatment are compared at specific points during a trial. If one treatment is found superior, the trial is stopped so that the most volunteers receive the more beneficial treatment.  This video helps explain randomization for all clinical trials .

" Blinded " (or " masked ") studies are designed to prevent members of the research team and study participants from influencing the results. Blinding allows the collection of scientifically accurate data. In single-blind (" single-masked ") studies, you are not told what is being given, but the research team knows. In a double-blind study, neither you nor the research team are told what you are given; only the pharmacist knows. Members of the research team are not told which participants are receiving which treatment, in order to reduce bias. If medically necessary, however, it is always possible to find out which treatment you are receiving.

Who takes part in clinical trials?

Many different types of people take part in clinical trials. Some are healthy, while others may have illnesses. Research procedures with healthy volunteers are designed to develop new knowledge, not to provide direct benefit to those taking part. Healthy volunteers have always played an important role in research.

Healthy volunteers are needed for several reasons. When developing a new technique, such as a blood test or imaging device, healthy volunteers help define the limits of "normal." These volunteers are the baseline against which patient groups are compared and are often matched to patients on factors such as age, gender, or family relationship. They receive the same tests, procedures, or drugs the patient group receives. Researchers learn about the disease process by comparing the patient group to the healthy volunteers.

Factors like how much of your time is needed, discomfort you may feel, or risk involved depends on the trial. While some require minimal amounts of time and effort, other studies may require a major commitment of your time and effort, and may involve some discomfort. The research procedure(s) may also carry some risk. The informed consent process for healthy volunteers includes a detailed discussion of the study's procedures and tests and their risks.

A patient volunteer has a known health problem and takes part in research to better understand, diagnose, or treat that disease or condition. Research with a patient volunteer helps develop new knowledge. Depending on the stage of knowledge about the disease or condition, these procedures may or may not benefit the study participants.

Patients may volunteer for studies similar to those in which healthy volunteers take part. These studies involve drugs, devices, or treatments designed to prevent,or treat disease. Although these studies may provide direct benefit to patient volunteers, the main aim is to prove, by scientific means, the effects and limitations of the experimental treatment. Therefore, some patient groups may serve as a baseline for comparison by not taking the test drug, or by receiving test doses of the drug large enough only to show that it is present, but not at a level that can treat the condition.

Researchers follow clinical trials guidelines when deciding who can participate, in a study. These guidelines are called Inclusion/Exclusion Criteria . Factors that allow you to take part in a clinical trial are called "inclusion criteria." Those that exclude or prevent participation are "exclusion criteria." These criteria are based on factors such as age, gender, the type and stage of a disease, treatment history, and other medical conditions. Before joining a clinical trial, you must provide information that allows the research team to determine whether or not you can take part in the study safely. Some research studies seek participants with illnesses or conditions to be studied in the clinical trial, while others need healthy volunteers. Inclusion and exclusion criteria are not used to reject people personally. Instead, the criteria are used to identify appropriate participants and keep them safe, and to help ensure that researchers can find new information they need.

What do I need to know if I am thinking about taking part in a clinical trial?

Risks and potential benefits

Clinical trials may involve risk, as can routine medical care and the activities of daily living. When weighing the risks of research, you can think about these important factors:

• The possible harms that could result from taking part in the study
• The level of harm
• The chance of any harm occurring

Most clinical trials pose the risk of minor discomfort, which lasts only a short time. However, some study participants experience complications that require medical attention. In rare cases, participants have been seriously injured or have died of complications resulting from their participation in trials of experimental treatments. The specific risks associated with a research protocol are described in detail in the informed consent document, which participants are asked to consider and sign before participating in research. Also, a member of the research team will explain the study and answer any questions about the study. Before deciding to participate, carefully consider risks and possible benefits.

Potential benefits

Well-designed and well-executed clinical trials provide the best approach for you to:

• Help others by contributing to knowledge about new treatments or procedures.
• Gain access to new research treatments before they are widely available.
• Receive regular and careful medical attention from a research team that includes doctors and other health professionals.

Risks to taking part in clinical trials include the following:

• There may be unpleasant, serious, or even life-threatening effects of experimental treatment.
• The study may require more time and attention than standard treatment would, including visits to the study site, more blood tests, more procedures, hospital stays, or complex dosage schedules.

What questions should I ask if offered a clinical trial?

If you are thinking about taking part in a clinical trial, you should feel free to ask any questions or bring up any issues concerning the trial at any time. The following suggestions may give you some ideas as you think about your own questions.

• What is the purpose of the study?
• Why do researchers think the approach may be effective?
• Who will fund the study?
• Who has reviewed and approved the study?
• How are study results and safety of participants being monitored?
• How long will the study last?
• What will my responsibilities be if I take part?
• Who will tell me about the results of the study and how will I be informed?

Risks and possible benefits

• What are my possible short-term benefits?
• What are my possible long-term benefits?
• What are my short-term risks, and side effects?
• What are my long-term risks?
• What other options are available?
• How do the risks and possible benefits of this trial compare with those options?

Participation and care

• What kinds of therapies, procedures and/or tests will I have during the trial?
• Will they hurt, and if so, for how long?
• How do the tests in the study compare with those I would have outside of the trial?
• Will I be able to take my regular medications while taking part in the clinical trial?
• Where will I have my medical care?
• Who will be in charge of my care?

Personal issues

• How could being in this study affect my daily life?
• Can I talk to other people in the study?

Cost issues

• Will I have to pay for any part of the trial such as tests or the study drug?
• If so, what will the charges likely be?
• What is my health insurance likely to cover?
• Who can help answer any questions from my insurance company or health plan?
• Will there be any travel or child care costs that I need to consider while I am in the trial?

Tips for asking your doctor about trials

• Consider taking a family member or friend along for support and for help in asking questions or recording answers.
• Plan what to ask — but don't hesitate to ask any new questions.
• Write down questions in advance to remember them all.
• Write down the answers so that they’re available when needed.
• Ask about bringing a tape recorder to make a taped record of what's said (even if you write down answers).

This information courtesy of Cancer.gov.

How is my safety protected?

Ethical guidelines

The goal of clinical research is to develop knowledge that improves human health or increases understanding of human biology. People who take part in clinical research make it possible for this to occur. The path to finding out if a new drug is safe or effective is to test it on patients in clinical trials. The purpose of ethical guidelines is both to protect patients and healthy volunteers, and to preserve the integrity of the science.

Informed consent

Informed consent is the process of learning the key facts about a clinical trial before deciding whether to participate. The process of providing information to participants continues throughout the study. To help you decide whether to take part, members of the research team explain the study. The research team provides an informed consent document, which includes such details about the study as its purpose, duration, required procedures, and who to contact for various purposes. The informed consent document also explains risks and potential benefits.

If you decide to enroll in the trial, you will need to sign the informed consent document. You are free to withdraw from the study at any time.

Most, but not all, clinical trials in the United States are approved and monitored by an Institutional Review Board (IRB) to ensure that the risks are minimal when compared with potential benefits. An IRB is an independent committee that consists of physicians, statisticians, and members of the community who ensure that clinical trials are ethical and that the rights of participants are protected. You should ask the sponsor or research coordinator whether the research you are considering participating in was reviewed by an IRB.

Further reading

For more information about research protections, see:

• Office of Human Research Protection
• Children's Assent to Clinical Trial Participation

For more information on participants’ privacy and confidentiality, see:

• HIPAA Privacy Rule
• The Food and Drug Administration, FDA’s Drug Review Process: Ensuring Drugs Are Safe and Effective

For more information about research protections, see: About Research Participation

What happens after a clinical trial is completed?

After a clinical trial is completed, the researchers carefully examine information collected during the study before making decisions about the meaning of the findings and about the need for further testing. After a phase I or II trial, the researchers decide whether to move on to the next phase or to stop testing the treatment or procedure because it was unsafe or not effective. When a phase III trial is completed, the researchers examine the information and decide whether the results have medical importance.

Results from clinical trials are often published in peer-reviewed scientific journals. Peer review is a process by which experts review the report before it is published to ensure that the analysis and conclusions are sound. If the results are particularly important, they may be featured in the news, and discussed at scientific meetings and by patient advocacy groups before or after they are published in a scientific journal. Once a new approach has been proven safe and effective in a clinical trial, it may become a new standard of medical practice.

Ask the research team members if the study results have been or will be published. Published study results are also available by searching for the study's official name or Protocol ID number in the National Library of Medicine's PubMed® database .

How does clinical research make a difference to me and my family?

Only through clinical research can we gain insights and answers about the safety and effectiveness of treatments and procedures. Groundbreaking scientific advances in the present and the past were possible only because of participation of volunteers, both healthy and those with an illness, in clinical research. Clinical research requires complex and rigorous testing in collaboration with communities that are affected by the disease. As research opens new doors to finding ways to diagnose, prevent, treat, or cure disease and disability, clinical trial participation is essential to help us find the answers.

This page last reviewed on October 3, 2022

Connect with Us

• More Social Media from NIH

Evidence-Based Medicine: Types of Studies

• What is Evidence-Based Practice?
• Question Types and Corresponding Resources
• Types of Studies
• Practice Guidelines
• Step 3: Appraise This link opens in a new window
• Steps 4-5: Apply & Assess

Experimental vs. Observational Studies

An observational study is a study in which the investigator cannot control the assignment of treatment to subjects because the participants or conditions are not directly assigned by the researcher.

• Examines predetermined treatments, interventions, policies, and their effects
• Four main types: case series , case-control studies , cross-sectional studies , and cohort studies

In an experimental study , the investigators directly manipulate or assign participants to different interventions or environments

Experimental studies that involve humans are called clinical trials . They fall into two categories: those with controls, and those without controls.

• Controlled trials - studies in which the experimental drug or procedure is compared with another drug or procedure
• Uncontrolled trials - studies in which the investigators' experience with the experimental drug or procedure is described, but the treatment is not compared with another treatment

Definitions taken from: Dawson B, Trapp R.G. (2004). Chapter 2. Study Designs in Medical Research. In Dawson B, Trapp R.G. (Eds), Basic & Clinical Biostatistics, 4e . Retrieved September 15, 2014 from  https://accessmedicine.mhmedical.com/book.aspx?bookid=2724

Levels of Evidence Pyramid

Levels of Evidence Pyramid created by Andy Puro, September 2014

Additional Study Design Resources

Study Design 101 : Himmelfarb's tutorial on study types and how to find them

Study Designs  (Centre for Evidence Based Medicine, University of Oxford)

Learn about Clinical Studies  (ClinicalTrials.gov, National Institutes of Health)

Study Designs Guide  (Deakin University)

• << Previous: Step 2: Acquire
• Next: Practice Guidelines >>

• Last Updated: Jul 1, 2024 9:31 AM
• URL: https://guides.himmelfarb.gwu.edu/ebm

• Himmelfarb Intranet
• Privacy Notice
• Terms of Use
• GW is committed to digital accessibility. If you experience a barrier that affects your ability to access content on this page, let us know via the Accessibility Feedback Form .
• Himmelfarb Health Sciences Library
• 2300 Eye St., NW, Washington, DC 20037
• Phone: (202) 994-2962
• [email protected]
• https://himmelfarb.gwu.edu

Transforming the understanding and treatment of mental illnesses.

Información en español

Celebrating 75 Years! Learn More >>

• Science News
• Meetings and Events
• Social Media
• Press Resources
• Email Updates
• Innovation Speaker Series

What are the different types of clinical research?

February 18, 2021

There are many different types of clinical research because researchers study many different things.  

Treatment research usually tests an intervention such as medication, psychotherapy, new devices, or new approaches.

Prevention research looks for better ways to prevent disorders from developing or returning. Different kinds of prevention research may study medicines, vitamins, or lifestyle changes.  

Diagnostic research refers to the practice of looking for better ways to identify a particular disorder or condition.  

Screening research aims to find the best ways to detect certain disorders or health conditions. 

Genetic studies aim to improve our ability to predict disorders by identifying and understanding how genes and illnesses may be related. Research in this area may explore ways in which a person’s genes make him or her more or less likely to develop a disorder. This may lead to development of tailor-made treatments based on a patient’s genetic make-up.  

Epidemiological studies look at how often and why disorders happen in certain groups of people.

Research studies can be outpatient or inpatient. Outpatient means that participants do not stay overnight at the hospital or research center. Inpatient means that participants will need to stay at least one night in the hospital or research center.  

Thank you for your interest in learning more about clinical research!

Types of Study Design

• 📖 Geeky Medics OSCE Book
• ⚡ Geeky Medics Bundles
• ✨ 1300+ OSCE Stations
• ✅ OSCE Checklist PDF Booklet
• 🧠 UKMLA AKT Question Bank
• 💊 PSA Question Bank
• 💉 Clinical Skills App
• 🗂️ Flashcard Collections | OSCE , Medicine , Surgery , Anatomy
• 💬 SCA Cases for MRCGP

To be the first to know about our latest videos subscribe to our YouTube channel 🙌

Table of Contents

Suggest an improvement

• Hidden Post Title
• Hidden Post URL
• Hidden Post ID
• Type of issue * N/A Fix spelling/grammar issue Add or fix a link Add or fix an image Add more detail Improve the quality of the writing Fix a factual error
• Please provide as much detail as possible * You don't need to tell us which article this feedback relates to, as we automatically capture that information for you.
• Your Email (optional) This allows us to get in touch for more details if required.
• Which organ is responsible for pumping blood around the body? * Enter a five letter word in lowercase
• Comments This field is for validation purposes and should be left unchanged.

Introduction

Study designs are frameworks used in medical research to gather data and explore a specific research question .

Choosing an appropriate study design is one of many essential considerations before conducting research to minimise bias and yield valid results .

This guide provides a summary of study designs commonly used in medical research, their characteristics, advantages and disadvantages.

Case-report and case-series

A case report is a detailed description of a patient’s medical history, diagnosis, treatment, and outcome. A case report typically documents unusual or rare cases or reports  new or unexpected clinical findings .

A case series is a similar study that involves a group of patients sharing a similar disease or condition. A case series involves a comprehensive review of medical records for each patient to identify common features or disease patterns. Case series help better understand a disease’s presentation, diagnosis, and treatment.

While a case report focuses on a single patient, a case series involves a group of patients to provide a broader perspective on a specific disease. Both case reports and case series are important tools for understanding rare or unusual diseases .

Advantages of case series and case reports include:

• Able to describe rare or poorly understood conditions or diseases
• Helpful in generating hypotheses and identifying patterns or trends in patient populations
• Can be conducted relatively quickly and at a lower cost compared to other research designs

Disadvantages

Disadvantages of case series and case reports include:

• Prone to selection bias , meaning that the patients included in the series may not be representative of the general population
• Lack a control group, which makes it difficult to conclude  the effectiveness of different treatments or interventions
• They are descriptive and cannot establish causality or control for confounding factors

Cross-sectional study

A cross-sectional study aims to measure the prevalence or frequency of a disease in a population at a specific point in time. In other words, it provides a “ snapshot ” of the population at a single moment in time.

Cross-sectional studies are unique from other study designs in that they collect data on the exposure and the outcome of interest from a sample of individuals in the population. This type of data is used to investigate the distribution of health-related conditions and behaviours in different populations, which is especially useful for guiding the development of public health interventions .

Example of a cross-sectional study

A cross-sectional study might investigate the prevalence of hypertension (the outcome) in a sample of adults in a particular region. The researchers would measure blood pressure levels in each participant and gather information on other factors that could influence blood pressure, such as age, sex, weight, and lifestyle habits (exposure).

Advantages of cross-sectional studies include:

• Relatively quick and inexpensive to conduct compared to other study designs, such as cohort or case-control studies
• They can provide a snapshot of the prevalence and distribution of a particular health condition in a population
• They can help to identify patterns and associations between exposure and outcome variables, which can be used to generate hypotheses for further research

Disadvantages of cross-sectional studies include:

• They cannot establish causality , as they do not follow participants over time and cannot determine the temporal sequence between exposure and outcome
• Prone to selection bias , as the sample may not represent the entire population being studied
• They cannot account for confounding variables , which may affect the relationship between the exposure and outcome of interest

Case-control study

A case-control study compares people who have developed a disease of interest ( cases ) with people who have not developed the disease ( controls ) to identify potential risk factors associated with the disease.

Once cases and controls have been identified, researchers then collect information about related risk factors , such as age, sex, lifestyle factors, or environmental exposures, from individuals. By comparing the prevalence of risk factors between the cases and the controls, researchers can determine the association between the risk factors and the disease.

Example of a case-control study

A case-control study design might involve comparing a group of individuals with lung cancer (cases) to a group of individuals without lung cancer (controls) to assess the association between smoking (risk factor) and the development of lung cancer.

Advantages of case-control studies include:

• Useful for studying rare diseases , as they allow researchers to selectively recruit cases with the disease of interest
• Useful for investigating potential risk factors for a disease, as the researchers can collect data on many different factors from both cases and controls
• Can be helpful in situations where it is not ethical or practical to manipulate exposure levels or randomise study participants

Disadvantages of case-control studies include:

• Prone to selection bias , as the controls may not be representative of the general population or may have different underlying risk factors than the cases
• Cannot establish causality , as they can only identify associations between factors and disease
• May be limited by the availability of suitable controls , as finding appropriate controls who have similar characteristics to the cases can be challenging

Cohort study

A cohort study follows a group of individuals (a cohort) over time to investigate the relationship between an exposure or risk factor and a particular outcome or health condition. Cohort studies can be further classified into prospective or retrospective cohort studies.

Prospective cohort study

A prospective cohort study is a study in which the researchers select a group of individuals who do not have a particular disease or outcome of interest at the start of the study.

They then follow this cohort over time to track the number of patients who develop the outcome . Before the start of the study, information on exposure(s) of interest may also be collected.

Example of a prospective cohort study

A prospective cohort study might follow a group of individuals who have never smoked and measure their exposure to tobacco smoke over time to investigate the relationship between smoking and lung cancer .

Retrospective cohort study

In contrast, a retrospective cohort study is a study in which the researchers select a group of individuals who have already been exposed to something (e.g. smoking) and look back in time (for example, through patient charts) to see if they developed the outcome (e.g. lung cancer ).

The key difference in retrospective cohort studies is that data on exposure and outcome are collected after the outcome has occurred.

Example of a retrospective cohort study

A retrospective cohort study might look at the medical records of smokers and see if they developed a particular adverse event such as lung cancer.

Advantages of cohort studies include:

• Generally considered to be the most appropriate study design for investigating the temporal relationship between exposure and outcome
• Can provide estimates of incidence and relative risk , which are useful for quantifying the strength of the association between exposure and outcome
• Can be used to investigate multiple outcomes or endpoints associated with a particular exposure, which can help to identify unexpected effects or outcomes

Disadvantages of cohort studies include:

• Can be expensive and time-consuming to conduct, particularly for long-term follow-up
• May suffer from selection bias , as the sample may not be representative of the entire population being studied
• May suffer from attrition bias , as participants may drop out or be lost to follow-up over time

Meta-analysis

A meta-analysis is a type of study that involves extracting outcome data from all relevant studies in the literature and combining the results of multiple studies to produce an overall estimate of the effect size of an intervention or exposure.

Meta-analysis is often conducted alongside a systematic review and can be considered a study of studies . By doing this, researchers provide a more comprehensive and reliable estimate of the overall effect size and their confidence interval (a measure of precision).

Meta-analyses can be conducted for a wide range of research questions , including evaluating the effectiveness of medical interventions, identifying risk factors for disease, or assessing the accuracy of diagnostic tests. They are particularly useful when the results of individual studies are inconsistent or when the sample sizes of individual studies are small, as a meta-analysis can provide a more precise estimate of the true effect size.

When conducting a meta-analysis, researchers must carefully assess the risk of bias in each study to enhance the validity of the meta-analysis. Many aspects of research studies are prone to bias , such as the methodology and the reporting of results. Where studies exhibit a high risk of bias, authors may opt to exclude the study from the analysis or perform a subgroup or sensitivity analysis.

Advantages of a meta-analysis include:

• Combine the results of multiple studies, resulting in a larger sample size and increased statistical power, to provide a more comprehensive and precise estimate of the effect size of an intervention or outcome
• Can help to identify sources of heterogeneity or variability in the results of individual studies by exploring the influence of different study characteristics or subgroups
• Can help to resolve conflicting results or controversies in the literature by providing a more robust estimate of the effect size

Disadvantages of a meta-analysis include:

• Susceptible to publication bias , where studies with statistically significant or positive results are more likely to be published than studies with nonsignificant or negative results. This bias can lead to an overestimation of the treatment effect in a meta-analysis
• May not be appropriate if the studies included are too heterogeneous , as this can make it difficult to draw meaningful conclusions from the pooled results
• Depend on the quality and completeness of the data available from the individual studies and may be limited by the lack of data on certain outcomes or subgroups

Ecological study

An ecological study assesses the relationship between outcome and exposure at a population level or among groups of people rather than studying individuals directly.

The main goal of an ecological study is to observe and analyse patterns or trends at the population level and to identify potential associations or correlations between environmental factors or exposures and health outcomes.

Ecological studies focus on collecting data on population health outcomes , such as disease or mortality rates, and environmental factors or exposures, such as air pollution, temperature, or socioeconomic status.

Example of an ecological study

An ecological study might be used when comparing smoking rates and lung cancer incidence across different countries.

Advantages of an ecological study include:

• Provide insights into how social, economic, and environmental factors may impact health outcomes in real-world settings , which can inform public health policies and interventions
• Cost-effective and efficient, often using existing data or readily available data, such as data from national or regional databases

Disadvantages of an ecological study include:

• Ecological fallacy occurs when conclusions about individual-level associations are drawn from population-level differences
• Ecological studies rely on population-level (i.e. aggregate) rather than individual-level data; they cannot establish causal relationships between exposures and outcomes, as the studies do not account for differences or confounders at the individual level

Randomised controlled trial

A randomised controlled trial (RCT) is an important study design commonly used in medical research to determine the effectiveness of a treatment or intervention . It is considered the gold standard in research design because it allows researchers to draw cause-and-effect conclusions about the effects of an intervention.

In an RCT, participants are randomly assigned to two or more groups. One group receives the intervention being tested, such as a new drug or a specific medical procedure. In contrast, the other group is a control group and receives either no intervention or a placebo .

Randomisation ensures that each participant has an equal chance of being assigned to either group, thereby minimising selection bias . To reduce bias, an RCT often uses a technique called blinding , in which study participants, researchers, or analysts are kept unaware of participant assignment during the study. The participants are then followed over time, and outcome measures are collected and compared to determine if there is any statistical difference between the intervention and control groups.

Example of a randomised controlled trial

An RCT might be employed to evaluate the effectiveness of a new smoking cessation program in helping individuals quit smoking compared to the existing standard of care.

Advantages of an RCT include:

• Considered the most reliable study design for establishing causal relationships between interventions and outcomes and determining the effectiveness of interventions
• Randomisation of participants to intervention and control groups ensures that the groups are similar at the outset, reducing the risk of selection bias and enhancing internal validity
• Using a control group allows researchers to compare with the group that received the intervention while controlling for confounding factors

Disadvantages of an RCT include:

• Can raise ethical concerns ; for example, it may be considered unethical to withhold an intervention from a control group, especially if the intervention is known to be effective
• Can be expensive and time-consuming to conduct, requiring resources for participant recruitment, randomisation, data collection, and analysis
• Often have strict inclusion and exclusion criteria , which may limit the generalisability of the findings to broader populations
• May not always be feasible or practical for certain research questions, especially in rare diseases or when studying long-term outcomes

Dr Chris Jefferies

• Yuliya L, Qazi MA (eds.). Toronto Notes 2022. Toronto: Toronto Notes for Medical Students Inc; 2022.
• Le T, Bhushan V, Qui C, Chalise A, Kaparaliotis P, Coleman C, Kallianos K. First Aid for the USMLE Step 1 2023. New York: McGraw-Hill Education; 2023.
• Rothman KJ, Greenland S, Lash T. Modern Epidemiology. 3 rd ed. Philadelphia: Lippincott Williams & Wilkins; 2008.

Other pages

• Product Bundles 🎉
• Join the Team 🙌
• Institutional Licence 📚
• OSCE Station Creator Tool 🩺
• Create and Share Flashcards 🗂️
• OSCE Group Chat 💬
• Newsletter 📰
• Advertise With Us

Join the community

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

• Publications
• Account settings
• My Bibliography
• Collections
• Citation manager

Save citation to file

Email citation, add to collections.

• Create a new collection
• Add to an existing collection

Add to My Bibliography

Your saved search, create a file for external citation management software, your rss feed.

• Search in PubMed
• Search in NLM Catalog
• Add to Search

Types of study in medical research: part 3 of a series on evaluation of scientific publications

Affiliation.

• 1 MDK Rheinland-Pfalz Referat Rehabilitation/Biometrie Albiger Str. 19 d 55232 Alzey, Germany. [email protected]
• PMID: 19547627
• PMCID: PMC2689572
• DOI: 10.3238/arztebl.2009.0262

Background: The choice of study type is an important aspect of the design of medical studies. The study design and consequent study type are major determinants of a study's scientific quality and clinical value.

Methods: This article describes the structured classification of studies into two types, primary and secondary, as well as a further subclassification of studies of primary type. This is done on the basis of a selective literature search concerning study types in medical research, in addition to the authors' own experience.

Results: Three main areas of medical research can be distinguished by study type: basic (experimental), clinical, and epidemiological research. Furthermore, clinical and epidemiological studies can be further subclassified as either interventional or noninterventional.

Conclusions: The study type that can best answer the particular research question at hand must be determined not only on a purely scientific basis, but also in view of the available financial resources, staffing, and practical feasibility (organization, medical prerequisites, number of patients, etc.).

Keywords: basic research; clinical research; epidemiology; literature search; study type.

PubMed Disclaimer

Classification of different study types…

Classification of different study types *1 , sometimes known as experimental research; *2…

Graphical depiction of a prospective…

Graphical depiction of a prospective cohort study (simplest case [2a]) and a retrospective…

Similar articles

• Study design in medical research: part 2 of a series on the evaluation of scientific publications. Röhrig B, du Prel JB, Blettner M. Röhrig B, et al. Dtsch Arztebl Int. 2009 Mar;106(11):184-9. doi: 10.3238/arztebl.2009.0184. Epub 2009 Mar 13. Dtsch Arztebl Int. 2009. PMID: 19568374 Free PMC article. Review.
• Folic acid supplementation and malaria susceptibility and severity among people taking antifolate antimalarial drugs in endemic areas. Crider K, Williams J, Qi YP, Gutman J, Yeung L, Mai C, Finkelstain J, Mehta S, Pons-Duran C, Menéndez C, Moraleda C, Rogers L, Daniels K, Green P. Crider K, et al. Cochrane Database Syst Rev. 2022 Feb 1;2(2022):CD014217. doi: 10.1002/14651858.CD014217. Cochrane Database Syst Rev. 2022. PMID: 36321557 Free PMC article.
• Critical assessment of progress of medical sciences in Iran and Turkey: the way developing countries with limited resources should make effective contributions to the production of science. Massarrat S, Kolahdoozan S. Massarrat S, et al. Arch Iran Med. 2011 Nov;14(6):370-7. Arch Iran Med. 2011. PMID: 22039839
• Scientific journals and their authors' financial interests: a pilot study. Krimsky S, Rothenberg LS, Stott P, Kyle G. Krimsky S, et al. Psychother Psychosom. 1998 Jul-Oct;67(4-5):194-201. doi: 10.1159/000012281. Psychother Psychosom. 1998. PMID: 9693346
• Public sector reforms and their impact on the level of corruption: A systematic review. Mugellini G, Della Bella S, Colagrossi M, Isenring GL, Killias M. Mugellini G, et al. Campbell Syst Rev. 2021 May 24;17(2):e1173. doi: 10.1002/cl2.1173. eCollection 2021 Jun. Campbell Syst Rev. 2021. PMID: 37131927 Free PMC article. Review.
• How to present and summarize a scientific journal article. Cox T, Columbus C, Ahmed K, Higginbotham J. Cox T, et al. Proc (Bayl Univ Med Cent). 2024 Jul 8;37(5):884-887. doi: 10.1080/08998280.2024.2371766. eCollection 2024. Proc (Bayl Univ Med Cent). 2024. PMID: 39165817 Free PMC article.
• Regression Analyses and Their Particularities in Observational Studies. Zapf A, Wiessner C, König IR. Zapf A, et al. Dtsch Arztebl Int. 2024 Feb 23;121(4):128-134. doi: 10.3238/arztebl.m2023.0278. Dtsch Arztebl Int. 2024. PMID: 38231741 Free PMC article. Review.
• The Role of AI in Serious Games and Gamification for Health: Scoping Review. Tolks D, Schmidt JJ, Kuhn S. Tolks D, et al. JMIR Serious Games. 2024 Jan 15;12:e48258. doi: 10.2196/48258. JMIR Serious Games. 2024. PMID: 38224472 Free PMC article. Review.
• Hotspots and frontiers of the relationship between gastric cancer and depression: A bibliometric study. Liu JY, Zheng JQ, Yin CL, Tang WP, Zhang JN. Liu JY, et al. World J Gastroenterol. 2023 Dec 14;29(46):6076-6088. doi: 10.3748/wjg.v29.i46.6076. World J Gastroenterol. 2023. PMID: 38130743 Free PMC article.
• Factors associated with the effectiveness of immersive virtual therapy in alleviating depressive symptoms during sub-acute post-stroke rehabilitation: a gender comparison. Juszko K, Kiper P, Wrzeciono A, Cieślik B, Gajda R, Szczepańska-Gieracha J. Juszko K, et al. BMC Sports Sci Med Rehabil. 2023 Oct 20;15(1):137. doi: 10.1186/s13102-023-00742-z. BMC Sports Sci Med Rehabil. 2023. PMID: 37864252 Free PMC article.
• Bortz J, Döring N. Forschungsmethoden und Evaluation. Springer: Berlin, Heidelberg, New York; 2002. pp. 39–84.
• Bortz J, Döring N. Forschungsmethoden und Evaluation. Berlin, Heidelberg, New York: Springer; 2002. 37 pp.
• Fletcher RH, Fletcher SW. Klinische Epidemiologie. Grundlagen und Anwendung. Bern: Huber; 2007. pp. 1–327.
• Altman DG. Practical statistics for medical research. 1. Aufl. Boca Raton, London, New York, Washington D.C.: Chapman & Hall; 1991. pp. 1–499.
• Schumacher M, Schulgen G. Methodik klinischer Studien. 2. Aufl. Berlin, Heidelberg, New York: Springer; 2007. pp. 1–436.
• Search in MeSH

Related information

• Cited in Books

LinkOut - more resources

Full text sources.

• Deutsches Aerzteblatt International
• Europe PubMed Central
• PubMed Central
• MedlinePlus Health Information

• Citation Manager

NCBI Literature Resources

MeSH PMC Bookshelf Disclaimer

The PubMed wordmark and PubMed logo are registered trademarks of the U.S. Department of Health and Human Services (HHS). Unauthorized use of these marks is strictly prohibited.

Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

Study designs

This short article gives a brief guide to the different study types and a comparison of the advantages and disadvantages.

See also  Levels of Evidence  

These study designs all have similar components (as we’d expect from the PICO):

• A defined population (P) from which groups of subjects are studied
• Outcomes (O) that are measured

And for experimental and analytic observational studies:

• Interventions (I) or exposures (E) that are applied to different groups of subjects

Overview of the design tree

Figure 1 shows the tree of possible designs, branching into subgroups of study designs by whether the studies are descriptive or analytic and by whether the analytic studies are experimental or observational. The list is not completely exhaustive but covers most basics designs.

Figure: Tree of different types of studies (Q1, 2, and 3 refer to the three questions below)

> Download a PDF by Jeremy Howick about study designs

Our first distinction is whether the study is analytic or non-analytic. A  non-analytic  or  descriptive  study does not try to quantify the relationship but tries to give us a picture of what is happening in a population, e.g., the prevalence, incidence, or experience of a group. Descriptive studies include case reports, case-series, qualitative studies and surveys (cross-sectional) studies, which measure the frequency of several factors, and hence the size of the problem. They may sometimes also include analytic work (comparing factors “” see below).

An  analytic  study attempts to quantify the relationship between two factors, that is, the effect of an intervention (I) or exposure (E) on an outcome (O). To quantify the effect we will need to know the rate of outcomes in a comparison (C) group as well as the intervention or exposed group. Whether the researcher actively changes a factor or imposes uses an intervention determines whether the study is considered to be observational (passive involvement of researcher), or experimental (active involvement of researcher).

In  experimental  studies, the researcher manipulates the exposure, that is he or she allocates subjects to the intervention or exposure group. Experimental studies, or randomised controlled trials (RCTs), are similar to experiments in other areas of science. That is, subjects are allocated to two or more groups to receive an intervention or exposure and then followed up under carefully controlled conditions. Such studies controlled trials, particularly if randomised and blinded, have the potential to control for most of the biases that can occur in scientific studies but whether this actually occurs depends on the quality of the study design and implementation.

In  analytic observational  studies, the researcher simply measures the exposure or treatments of the groups. Analytical observational studies include case””control studies, cohort studies and some population (cross-sectional) studies. These studies all include matched groups of subjects and assess of associations between exposures and outcomes.

Observational studies investigate and record exposures (such as interventions or risk factors) and observe outcomes (such as disease) as they occur. Such studies may be purely descriptive or more analytical.

We should finally note that studies can incorporate several design elements. For example, a the control arm of a randomised trial may also be used as a cohort study; and the baseline measures of a cohort study may be used as a cross-sectional study.

Spotting the study design

The type of study can generally be worked at by looking at three issues (as per the Tree of design in Figure 1):

Q1. What was the aim of the study?

• To simply describe a population (PO questions) descriptive
• To quantify the relationship between factors (PICO questions) analytic.

Q2. If analytic, was the intervention randomly allocated?

• No? Observational study

For observational study the main types will then depend on the timing of the measurement of outcome, so our third question is:

Q3. When were the outcomes determined?

• Some time after the exposure or intervention? cohort study (‘prospective study’)
• At the same time as the exposure or intervention? cross sectional study or survey
• Before the exposure was determined? case-control study (‘retrospective study’ based on recall of the exposure)

Advantages and Disadvantages of the Designs

Randomised Controlled Trial

An experimental comparison study in which participants are allocated to treatment/intervention or control/placebo groups using a random mechanism (see randomisation). Best for study the effect of an intervention.

Advantages:

• unbiased distribution of confounders;
• blinding more likely;
• randomisation facilitates statistical analysis.

Disadvantages:

• expensive: time and money;
• volunteer bias;
• ethically problematic at times.

Crossover Design

A controlled trial where each study participant has both therapies, e.g, is randomised to treatment A first, at the crossover point they then start treatment B. Only relevant if the outcome is reversible with time, e.g, symptoms.

• all subjects serve as own controls and error variance is reduced thus reducing sample size needed;
• all subjects receive treatment (at least some of the time);
• statistical tests assuming randomisation can be used;
• blinding can be maintained.
• all subjects receive placebo or alternative treatment at some point;
• washout period lengthy or unknown;
• cannot be used for treatments with permanent effects

Cohort Study

Data are obtained from groups who have been exposed, or not exposed, to the new technology or factor of interest (eg from databases). No allocation of exposure is made by the researcher. Best for study the effect of predictive risk factors on an outcome.

• ethically safe;
• subjects can be matched;
• can establish timing and directionality of events;
• eligibility criteria and outcome assessments can be standardised;
• administratively easier and cheaper than RCT.
• controls may be difficult to identify;
• exposure may be linked to a hidden confounder;
• blinding is difficult;
• randomisation not present;
• for rare disease, large sample sizes or long follow-up necessary.

Case-Control Studies

Patients with a certain outcome or disease and an appropriate group of controls without the outcome or disease are selected (usually with careful consideration of appropriate choice of controls, matching, etc) and then information is obtained on whether the subjects have been exposed to the factor under investigation.

• quick and cheap;
• only feasible method for very rare disorders or those with long lag between exposure and outcome;
• fewer subjects needed than cross-sectional studies.
• reliance on recall or records to determine exposure status;
• confounders;
• selection of control groups is difficult;
• potential bias: recall, selection.

Cross-Sectional Survey

A study that examines the relationship between diseases (or other health-related characteristics) and other variables of interest as they exist in a defined population at one particular time (ie exposure and outcomes are both measured at the same time). Best for quantifying the prevalence of a disease or risk factor, and for quantifying the accuracy of a diagnostic test.

• cheap and simple;
• ethically safe.
• establishes association at most, not causality;
• recall bias susceptibility;
• confounders may be unequally distributed;
• Neyman bias;
• group sizes may be unequal.

COLUMBIA UNIVERSITY IN THE CITY OF NEW YORK

Clinical Research Coordinator - Cardiology

• Columbia University Medical Center
• Opening on: Sep 11 2024
• Job Type: Officer of Administration
• Regular/Temporary: Regular
• Hours Per Week: 35
• Salary Range: $62,400 - $65,000 Annual

Position Summary

The Clinical Research Coordinator provides research coordination support for multiple clinical research projects.  The primary focus of this role is to assist with the coordination of studies rather than independently managing clinical trials.  The position involves coordinating various clinical research projects, such as registries, retrospective data reviews, long-term follow-up studies, and other non-interventional studies.

Responsibilities

Clinical Research Responsibilities:

• Screen participants for study eligibility and accurately enroll them in various databases.
• Perform simple study procedures with accuracy.
• Understand the structure of study protocols and interpret study requirements to ensure compliance.
• Follow proper documentation techniques as outlined in the ICH-GCP guidelines.
• Process subject reimbursement using pcards.
• Retrieve and utilize information from electronic medical records (EMR) and databases/CTMS/EDC.
• Maintain essential regulatory documents as required.
• Assist the research coordinator in the conduct of Site Initiation Visits (SIV) and attend monitor visits and audits.

Data Coordination Responsibilities:

• Collect basic demographic information during study visits.
• Enter data into forms (CRFs) on paper, databases, or electronic data capture systems (EDCs).
• Assist in collecting external medical records and radiology CDs as assigned.
• Administer minimal risk consents independently or complex consents under supervision.
• Conduct surveys and questionnaires.
• Verify the accuracy of own work and resolve simple queries.
• Perform concomitant medications abstraction.
• Build patient research study charts.
• Assist in quality control efforts, such as reviewing consents for signatures.

Regulatory Coordination Responsibilities:

• Collaborate with regulatory support to collect essential documents and maintain the regulatory binder (e.g., CVs, MD licenses, lab certifications, IRB rosters, lab norms).
• Assist with adverse events (AEs) and serious adverse events (SAEs).

Administrative Responsibilities:

• Demonstrate an understanding of the clinical research objectives associated with the program.
• Communicate with study participants by sending study correspondence via mail or email.
• Schedule subjects for research visits and follow-up appointments.
• Monitor study calendar for completion of study procedures.
• Manage study supply inventory.
• Utilize documents and systems to track recruitment and retention of participants.
• Work with regulatory support to maintain the regulatory binder.
• Gain appropriate training and knowledge of electronic medical records (EMR), clinical trial management systems (CTMS), electronic data capture (EDC), databases, and other relevant systems.
• Willingly learn and utilize available technology and systems to fulfill job requirements.
• Understand the disease process associated with the program.
• Attend and actively participate in all assigned training classes.
• Perform other responsibilities as assigned.

**Responsibilities may vary based on the specific needs of the unit or team. Some units/teams may require a proportionate focus on clinical, data, regulatory, or other specific needs. The Clinical Research Coordinator position will primarily support task-oriented needs.

Minimum Qualifications

• Bachelor's degree in Health Science or equivalent in education, training and experience.

Preferred Qualifications

• At least two years of related experience.
• Knowledge of university policies and procedures.
• Previous experience working in a large and complex healthcare setting.

Other Requirements

• Familiarity with medical terminology.
• Ability to communicate effectively with staff and faculty members at all levels.     
• Contact with patients and/or human research subjects
• Successful completion of applicable compliance and systems training requirements

Equal Opportunity Employer / Disability / Veteran

Columbia University is committed to the hiring of qualified local residents.

Commitment to Diversity 

Columbia university is dedicated to increasing diversity in its workforce, its student body, and its educational programs. achieving continued academic excellence and creating a vibrant university community require nothing less. in fulfilling its mission to advance diversity at the university, columbia seeks to hire, retain, and promote exceptionally talented individuals from diverse backgrounds.  , share this job.

Thank you - we'll send an email shortly.

Other Recently Posted Jobs

Research Project Coordinator

Assistant director, sexual violence response, clinical coordinator, mhp.

Refer someone to this job

• ©2022 Columbia University
• Accessibility
• Administrator Log in

Wait! Before you go, are you interested in a career at Columbia University? Sign up here! 

Thank you, for sharing your information. A member of our team will reach out to you soon!

This website uses cookies as well as similar tools and technologies to understand visitors' experiences. By continuing to use this website, you consent to Columbia University's usage of cookies and similar technologies, in accordance with the Columbia University Website Cookie Notice .

Study reveals how SARS-CoV-2 triggers diabetes by destroying pancreatic cells

• Download PDF Copy

Researchers from Weill Cornell Medicine have used a cutting-edge model system to uncover the mechanism by which SARS-CoV-2, the virus that causes COVID-19, induces new cases of diabetes, and worsens complications in people who already have it. The team found that viral exposure activates immune cells that in turn destroy beta (β) cells, the pancreatic cells that produce insulin. The study was published Sept. 2 in Cell Stem Cell.

There has long been a hypothesis in the field that certain viral infections may trigger type 1 diabetes. But we were able to show how this happens in the context of COVID-19 infection." Dr. Shuibing Chen, co-corresponding author,  director of the Center for Genomic Health, the Kilts Family Professor of Surgery and a member of the Hartman Institute for Therapeutic Organ Regeneration at Weill Cornell Medicine

"When someone has severe COVID-19, of course the first priority is to treat the life-threatening symptoms," said co-corresponding author Dr. Robert Schwartz, an associate professor of medicine at Weill Cornell Medicine and a gastroenterologist and hepatologist at NewYork-Presbyterian/Weill Cornell Medical Center. "But moving forward, there may be a way to develop clinical therapeutics that help avoid later injury to organs like the pancreas."

Dr. Liuliu Yang and Dr. Yuling Han, who were postdoctoral fellows in the Department of Surgery, and Dr. Tuo Zhang, an instructor in microbiology and immunology at Weill Cornell Medicine, were co-first authors of the paper.

From the early days of the COVID-19 pandemic, doctors caring for sick patients observed that the virus affected a number of organ systems, including not only the lungs, but also the heart, liver, colon and pancreas. For the current work, the researchers started with samples of pancreatic tissue from autopsies of people who had died of COVID-19. They observed that the pancreatic islets, the parts of the pancreas that generate the insulin to regulate blood sugar, were damaged.

Related Stories

• COVID-19 mRNA vaccine linked to myocardial scarring in adolescents and young adults
• Researchers uncover connection between two common diabetes drugs with implications for foot ulcer healing
• Scientists advance type 1 diabetes treatment with cutting-edge stem cell and gene editing technologies

They then used an analysis technique called GeoMx to study the samples in more detail. This revealed the presence of immune cells called proinflammatory macrophages in the tissues. The job of these macrophages is to kill off pathogens, but they sometimes cause collateral damage to healthy tissues.

To learn more about this activity, the team used a model system developed in the Chen Lab that had never been used before; pancreatic islet organoids (mini organs) that included both a vascular system and immune cells. "If we want to use organoids to study how a disease progresses, it's important to be able to include components of the immune system in these models," said Dr. Chen. In this case, after infecting the organoids with SARS-CoV-2, they found the macrophages appeared to be killing off the β cells through a type of cell death called pyroptosis.

The team also used the organoids to study how the pancreas responds to infection with another infectious virus — coxsackievirus B4, which has been implicated in the onset of type 1 diabetes. They found a similar macrophage response. "Moving forward, this organoid system is going to be useful for looking at other viruses as well," Dr. Schwartz said.

Further research on the signaling molecules that activate the macrophages also suggested potential interventions for protecting β cells from damage in patients with severe infections. Although it is too early to begin testing any treatments, this is something that may be possible in the future. This work could also help shed light on the underlying causes of long COVID, a condition that is believed to affect more than 15 million people in the United States.

Weill Cornell Medicine

Yang, L., et al . (2024). Human vascularized macrophage-islet organoids to model immune-mediated pancreatic β cell pyroptosis upon viral infection.  Cell Stem Cell . doi.org/10.1016/j.stem.2024.08.007 .

Posted in: Medical Science News | Medical Research News | Medical Condition News | Disease/Infection News

Tags: Blood , Blood Sugar , Cell , Cell Death , Colon , covid-19 , Diabetes , Genomic , Heart , Immune System , Immunology , Insulin , Kidney , Liver , Lungs , Macrophage , Medicine , Microbiology , Organoids , Pancreas , Pandemic , Research , SARS , SARS-CoV-2 , Surgery , Therapeutics , Type 1 Diabetes , Vascular , Virus

Suggested Reading

Cancel reply to comment

• Trending Stories
• Latest Interviews
• Top Health Articles

How can microdialysis benefit drug development

Ilona Vuist

In this interview, discover how Charles River uses the power of microdialysis for drug development as well as CNS therapeutics.

Global and Local Efforts to Take Action Against Hepatitis

Lindsey Hiebert and James Amugsi

In this interview, we explore global and local efforts to combat viral hepatitis with Lindsey Hiebert, Deputy Director of the Coalition for Global Hepatitis Elimination (CGHE), and James Amugsi, a Mandela Washington Fellow and Physician Assistant at Sandema Hospital in Ghana. Together, they provide valuable insights into the challenges, successes, and the importance of partnerships in the fight against hepatitis.

Addressing Important Cardiac Biology Questions with Shotgun Top-Down Proteomics

In this interview conducted at Pittcon 2024, we spoke to Professor John Yates about capturing cardiomyocyte cell-to-cell heterogeneity via shotgun top-down proteomics.

Latest News

Newsletters you may be interested in

Your AI Powered Scientific Assistant

Hi, I'm Azthena, you can trust me to find commercial scientific answers from News-Medical.net.

A few things you need to know before we start. Please read and accept to continue.

• Use of “Azthena” is subject to the terms and conditions of use as set out by OpenAI .
• Content provided on any AZoNetwork sites are subject to the site Terms & Conditions and Privacy Policy .
• Large Language Models can make mistakes. Consider checking important information.

Great. Ask your question.

Azthena may occasionally provide inaccurate responses. Read the full terms .

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions .

Provide Feedback

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

• Publications
• Account settings

Preview improvements coming to the PMC website in October 2024. Learn More or Try it out now .

• Advanced Search
• Journal List
• Perspect Clin Res
• v.9(4); Oct-Dec 2018

Study designs: Part 1 – An overview and classification

Priya ranganathan.

Department of Anaesthesiology, Tata Memorial Centre, Mumbai, Maharashtra, India

Rakesh Aggarwal

1 Department of Gastroenterology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India

There are several types of research study designs, each with its inherent strengths and flaws. The study design used to answer a particular research question depends on the nature of the question and the availability of resources. In this article, which is the first part of a series on “study designs,” we provide an overview of research study designs and their classification. The subsequent articles will focus on individual designs.

INTRODUCTION

Research study design is a framework, or the set of methods and procedures used to collect and analyze data on variables specified in a particular research problem.

Research study designs are of many types, each with its advantages and limitations. The type of study design used to answer a particular research question is determined by the nature of question, the goal of research, and the availability of resources. Since the design of a study can affect the validity of its results, it is important to understand the different types of study designs and their strengths and limitations.

There are some terms that are used frequently while classifying study designs which are described in the following sections.

A variable represents a measurable attribute that varies across study units, for example, individual participants in a study, or at times even when measured in an individual person over time. Some examples of variables include age, sex, weight, height, health status, alive/dead, diseased/healthy, annual income, smoking yes/no, and treated/untreated.

Exposure (or intervention) and outcome variables

A large proportion of research studies assess the relationship between two variables. Here, the question is whether one variable is associated with or responsible for change in the value of the other variable. Exposure (or intervention) refers to the risk factor whose effect is being studied. It is also referred to as the independent or the predictor variable. The outcome (or predicted or dependent) variable develops as a consequence of the exposure (or intervention). Typically, the term “exposure” is used when the “causative” variable is naturally determined (as in observational studies – examples include age, sex, smoking, and educational status), and the term “intervention” is preferred where the researcher assigns some or all participants to receive a particular treatment for the purpose of the study (experimental studies – e.g., administration of a drug). If a drug had been started in some individuals but not in the others, before the study started, this counts as exposure, and not as intervention – since the drug was not started specifically for the study.

Observational versus interventional (or experimental) studies

Observational studies are those where the researcher is documenting a naturally occurring relationship between the exposure and the outcome that he/she is studying. The researcher does not do any active intervention in any individual, and the exposure has already been decided naturally or by some other factor. For example, looking at the incidence of lung cancer in smokers versus nonsmokers, or comparing the antenatal dietary habits of mothers with normal and low-birth babies. In these studies, the investigator did not play any role in determining the smoking or dietary habit in individuals.

For an exposure to determine the outcome, it must precede the latter. Any variable that occurs simultaneously with or following the outcome cannot be causative, and hence is not considered as an “exposure.”

Observational studies can be either descriptive (nonanalytical) or analytical (inferential) – this is discussed later in this article.

Interventional studies are experiments where the researcher actively performs an intervention in some or all members of a group of participants. This intervention could take many forms – for example, administration of a drug or vaccine, performance of a diagnostic or therapeutic procedure, and introduction of an educational tool. For example, a study could randomly assign persons to receive aspirin or placebo for a specific duration and assess the effect on the risk of developing cerebrovascular events.

Descriptive versus analytical studies

Descriptive (or nonanalytical) studies, as the name suggests, merely try to describe the data on one or more characteristics of a group of individuals. These do not try to answer questions or establish relationships between variables. Examples of descriptive studies include case reports, case series, and cross-sectional surveys (please note that cross-sectional surveys may be analytical studies as well – this will be discussed in the next article in this series). Examples of descriptive studies include a survey of dietary habits among pregnant women or a case series of patients with an unusual reaction to a drug.

Analytical studies attempt to test a hypothesis and establish causal relationships between variables. In these studies, the researcher assesses the effect of an exposure (or intervention) on an outcome. As described earlier, analytical studies can be observational (if the exposure is naturally determined) or interventional (if the researcher actively administers the intervention).

Directionality of study designs

Based on the direction of inquiry, study designs may be classified as forward-direction or backward-direction. In forward-direction studies, the researcher starts with determining the exposure to a risk factor and then assesses whether the outcome occurs at a future time point. This design is known as a cohort study. For example, a researcher can follow a group of smokers and a group of nonsmokers to determine the incidence of lung cancer in each. In backward-direction studies, the researcher begins by determining whether the outcome is present (cases vs. noncases [also called controls]) and then traces the presence of prior exposure to a risk factor. These are known as case–control studies. For example, a researcher identifies a group of normal-weight babies and a group of low-birth weight babies and then asks the mothers about their dietary habits during the index pregnancy.

Prospective versus retrospective study designs

The terms “prospective” and “retrospective” refer to the timing of the research in relation to the development of the outcome. In retrospective studies, the outcome of interest has already occurred (or not occurred – e.g., in controls) in each individual by the time s/he is enrolled, and the data are collected either from records or by asking participants to recall exposures. There is no follow-up of participants. By contrast, in prospective studies, the outcome (and sometimes even the exposure or intervention) has not occurred when the study starts and participants are followed up over a period of time to determine the occurrence of outcomes. Typically, most cohort studies are prospective studies (though there may be retrospective cohorts), whereas case–control studies are retrospective studies. An interventional study has to be, by definition, a prospective study since the investigator determines the exposure for each study participant and then follows them to observe outcomes.

The terms “prospective” versus “retrospective” studies can be confusing. Let us think of an investigator who starts a case–control study. To him/her, the process of enrolling cases and controls over a period of several months appears prospective. Hence, the use of these terms is best avoided. Or, at the very least, one must be clear that the terms relate to work flow for each individual study participant, and not to the study as a whole.

Classification of study designs

Figure 1 depicts a simple classification of research study designs. The Centre for Evidence-based Medicine has put forward a useful three-point algorithm which can help determine the design of a research study from its methods section:[ 1 ]

Classification of research study designs

• Does the study describe the characteristics of a sample or does it attempt to analyze (or draw inferences about) the relationship between two variables? – If no, then it is a descriptive study, and if yes, it is an analytical (inferential) study
• If analytical, did the investigator determine the exposure? – If no, it is an observational study, and if yes, it is an experimental study
• If observational, when was the outcome determined? – at the start of the study (case–control study), at the end of a period of follow-up (cohort study), or simultaneously (cross sectional).

In the next few pieces in the series, we will discuss various study designs in greater detail.

Financial support and sponsorship

Conflicts of interest.

There are no conflicts of interest.