Final answer:
A retrospective cohort study is a research design that looks back in time to study the occurrence of an outcome. It compares a group of individuals with the outcome to a group without the outcome and analyzes the association between exposure and outcome.
Step-by-step explanation:
A retrospective cohort study is a type of research design in which the researcher looks back in time to study the occurrence of an outcome. In this design, a group of individuals who already have the outcome of interest (cases) is compared to a group of individuals who do not have the outcome (controls). The researchers collect data on both groups and analyze the association between exposure and outcome.
Retrospective cohort studies are useful when it is not feasible or ethical to conduct a prospective study. They are especially helpful for studying rare outcomes or long-term effects.