Nested case-control study
The drawback of nested case-control study is non-diseased persons from whom the controls are selected may not be fully representative of the original cohort due to death or losses to follow-up.
Nested case-control studies are case-control studies done in the population of an ongoing cohort study. The case-control study is thus said to be “nested” inside the cohort study. In large cohorts, it is often more efficient to construct a case-control study within the cohort, once a significant number of cases have emerged, to study a specific exposure not measured at baseline