What defines a retrospective cohort study?

A retrospective cohort study is characterized by its methodology of examining past records to define its cohorts. In this type of study, researchers look back at existing data sources—such as medical records, interviews, or other historical data—to identify subjects who were exposed to certain risk factors or treatments in the past and then analyze their outcomes. This allows researchers to establish a direct link between exposure and outcome using data that was recorded before the study began.

By relying on historical data, a retrospective cohort study can often be completed more quickly and with less expense than a prospective study, which involves following subjects forward in time from the point of exposure. The focus on past records is what fundamentally distinguishes a retrospective cohort study from other types of studies, making it a crucial aspect of its definition.