When Is Study Done?

Prospective and Retrospective

Prospective and retrospective refer to when the study is done in relation to the study base experience (other epidemiologists refer to concurrent and non-concurrent).

Retrospective

• A case-control study is carried out after the disease experience of the study base has already occurred or retrospectively.

• Cohorts can also be retrospective. Looking back in time, a group of individuals is identified as a cohort (a typical example is a group of workers, such as shipyard workers in WWII) and then their disease experience over a period of time is investigated.