Primer of Epidemiology IV. Study designs II: Interventional or experimental designs.

In this article, we describe experimental study designs and focus on randomized controlled trials. Experimental studies are intervention studies in which the investigator tests a new treatment on a selected group of patients. In a controlled design, the effects of an intervention (new treatment) are measured by comparing the outcome in the experimental group with that in a control group. Experimental studies are similar to cohort studies except that the exposure is a deliberate change (intervention) made by the researcher in one group of participants and it overcomes confounding because the treatment is assigned randomly. Further, we discuss various types of randomization (random sequence allocation) and importance of allocation concealment and blinding for proper assessment of outcomes in randomized trials.