Retrospective Nested Case-Control Study

A retrospective nested case-control study is an efficient observational design in which cases and matched controls are sampled from within an already-assembled retrospective cohort. Exposure data are retrieved from historical records only for selected participants, dramatically reducing data-collection costs while retaining most of the analytic power of the full cohort. It is widely used in pharmacoepidemiology, occupational health, and disease-registry research.