Prospective Nested Case-Control

A prospective nested case-control study enrolls a cohort before disease onset, follows participants forward in time, and then — once cases develop — samples matched controls from those still at risk at the time each case occurs. By embedding the case-control comparison inside a prospective cohort, the design combines the causal clarity of longitudinal follow-up with the cost efficiency of analysing only a fraction of the cohort's stored specimens or records.