Case–control study versus<unk>  on a timeline. "OR" stands for "odds ratio" and "RR" stands for "relative risk". A<unk> , also called a historic<unk>  study, is a longitudinal<unk>  study used in medical and psychological research. A<unk>  of individuals that share a common exposure factor is compared with another group of equivalent individuals not exposed to that factor, to determine the factor's influence on the incidence of a condition such as disease or death.<unk> es have existed for approximately as long as prospective<unk>  studies.
Retrospective cohort study
Natural history study
Prospective cohort study
Nested case–control study
Cohort study
Case–control study
Randomized controlled trial
Placebo-controlled study