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Cohort Study is an observational study in which a group of individuals â a cohort â are followed over a period of time in order to determine either the incidence rate of certain diseases or the risk factors that lead to those diseases. These studies can be either prospective or retrospective.
However, cohort studies are major undertakings. They may require long periods of follow-up since disease may occur a long time after exposure. Therefore, it is a very expensive study design. Cohort studies work well for rare exposuresâyou can specifically select people exposed to a certain factor.