Epidemiology

Studying the determinants of disease frequency falls within the domain of analytic epidemiology. The interest in causal relationships determines the type of study designs that epidemiologists employ. An experimental design is rarely appropriate to investigate disease etiology in humans: imagine the implications of randomly assigning individuals to smoke or not to smoke in order to study the effects on lung cancer. Therefore, epidemiologists must rely largely on observational study designs to determine association and to assess causation. The two most common observational study designs are the case-control study, in which individuals with and without the disease of interest are selected and prior exposure history is assessed, and the cohort study, in which individuals with and without the exposure of interest are selected and followed to determine the development of disease.