Cohort Study
Cohort Study
This is a investigation in which a cohort of individuals who do not have evidence of an outcome of interest but who are exposed to the putative cause are compared with a concurrent cohort who are also free of the outcome but not exposed to the putative cause. Both cohorts are then followed forward in time to compare the incidence of the outcome of interest. When used to study the effectiveness of an intervention, it is an investigation in which a cohort of individuals who receive the intervention are compared with a concurrent cohort who do not receive the intervention, wherein both cohorts are followed forward to compare the incidence of the outcome of interest. Cohort studies can be conducted retrospectively in the sense that someone other than the investigator has followed patients, and the investigator obtains the data base and then examines the association between exposure and outcome.