As I have said, analytic epidemiology falls outside the scope of this module. But I want to mention that there are two major kinds of analytic research designs in epidemiology: cohort and case-control. Randomized clinical trials and other kinds of intervention studies are a special case of the cohort design, whereby investigators manipulate subjects’ exposures, such as to different kinds of therapies. This experimental approach contrasts with observational epidemiology in which investigators do not seek to influence health outcomes via exposure history; that is, exposures are not forced in observational studies.