The primary goal of observational studies, e.g., case-control studies and cohort studies, is to test hypotheses about the determinants of disease. In contrast, the goal of intervention studies is to test the efficacy of specific treatments or preventive measures by assigning individual subjects to one of two or more treatment or prevention options. Intervention studies often test the efficacy of drugs, but one might also use this design to test the efficacy of differing management strategies or regimens. There are two major types of intervention studies:

In many respects the design of a clinical trial is analogous to a prospective cohort study, except that the investigators assign or allocate the exposure (treatment) under study.

This provides clinical trials with a powerful advantage over observational studies, provided the assignment to a treatment group is done randomly with a sufficiently large sample size. Under these circumstances randomized clinical trials (RCTs) provide the best opportunity to control for confounding and avoid certain biases. Consequently, they provide the most effective way to detect small to moderate benefits of one treatment over another. However, in order to provide definitive answers, clinical trials must enroll a sufficient number of appropriate subjects and follow them for an adequate period of time. Consequently, clinical trials can be long and expensive.

Learning Objectives

After successfully completing this section, the student will be able to: