Epidemiologic studies are also designed to identify risk factors that influence the base rates of diseases in the general population. Differential distribution by gender, age, ethnicity, geographic site, or by exposure to particular risk factors provides clues that may be tested systematically with case-control designs. These studies compare the association between a particular risk factor or disease correlate and the presence or absence of a given disease, after controlling for relevant confounding variables. Case-control studies generally proceed from retrospective designs defined by the presence or absence of a disease in the cases and controls, in order to identify potential associations between a particular risk factor or set of risk factors, and prospective cohort studies where the cases and controls are defined by the presence or absence of a putative risk factor, and followed prospectively to examine differential incidence of the disease.
