Cohort studies - prospective and retrospective

Prospective cohort studies

A prospective cohort study is where one or more samples (cohort) are followed prospectively and subsequent status evaluations with respect to a disease or outcome are conducted to determine which initial participants exposure characteristics (risk factors) are associated with it. The individual exposure status is known at the start of the study before the development of the disease. As the study is conducted, outcome from participants in each cohort is measured and relationships with specific characteristics determined.

Prospective cohort studies are superior to retrospective cohort studies.

Retrospective cohort studies

This is where the exposure status of the whole cohort (e.g. occupational cohort) is known from historical or occupational records and the disease status of individuals from the whole cohort is obtained in current time.

If we look at the following diagram, you can see clearly how prospective and retrospective studies differ.