In epidemiology, a cohort design or cohort study is a nonexperimental study design that involves comparing the occurrence of a disease or condition in two or more groups (or cohorts) of people that differ on a certain characteristic, risk factor, or exposure. The disease, state, or condition under study is often referred to as the outcome, whereas the characteristic, risk factor, or exposure is often referred to as the exposure. A cohort study is one of two principal types of nonexperimental study designs used to study the causes of disease. The other is the case–control design, in which cases of the disease under study are compared with respect to their past exposure with a similar group of individuals who do not have the disease.

Cohort (from ...