What is an experimental study?

An experimental study, sometimes called an intervention study, is a non-observational study where the investigator assigns the exposure (new drug, diet, programs, or intervention) to a group and follows the group over time to determine the relationship between the exposure and the outcome.

In experimental studies, if the exposure assignment is done randomly, this is a randomized control trial (the gold standard of study designs).

In this case, participants have an equal chance of being assigned to the experimental group or the control group.

To conduct experimental studies, you must have clinical equipoise. That is, there must be uncertainty about the exposure or treatment. Also, based on the Declaration of Helsinki, all study participants, including the controls, must have the best available treatment.

How are experimental studies different from cohort studies?

Experimental studies are different from cohort studies because the researcher assigns the exposure before following the exposed group(s) to assess the development of an outcome.


In open trials, everyone knows who is getting what treatment or exposure, but in single, double, and triple blinded studies neither the patient, investigator, or the statisticians know whether someone is the control or treatment group.

  • Single blind: the patient may be blinded to his/her exposure.
  • Double blind: the investigator may also be blind to the patient’s exposure.
  • Triple blind: the statistician may also be blind to the patient’s exposure.

Example of an experimental study

The Physicians’ Health Study (PHS) is an example of an experimental study. The goal of PHS is to assess the benefits or risks of aspirin and beta-carotene as a way of preventing cardiovascular disease and cancer.


Experimental studies provide an efficient way of controlling for confounders. With a large enough sample size, randomization will distribute known and unknown confounders equally in all groups.

Sometimes, out of necessity, you may need to move a control into the treatment group. In this case, Intention to treat analysis will be the only way to preserve randomization.

It is important to note that you will lose randomization if you move people around. However, all participants will still be analyzed in their initially assigned groups.


When conducting experimental studies, it is most important to consider ethics and compliance. Experimental studies can be costly to carry out, and data collection and analysis can be time-consuming.

Generalizability is often an issue with experimental studies, but this ultimately depends on who participates in the study.

Selection bias and misclassification are still possible in experimental studies. If participants in the control group drop out at differing rates than those in the experimental group, this can create potential problems for the study.

I hope this post is helpful to interested readers. I started MyStudentHq as a way to learn and write about what I learn. My foray into epidemiologic study designs on this site is related to my commitment to learning and writing boldly.

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