A researcher has banked serum samples from a cohort of 20,000 women enrolled 10 years ago. Women in whom breast cancer subsequently developed are identified, and for each such woman two cancer-free women matched on age and sampling date are selected from the remaining cohort members. Stored sera from these selected women are then assayed for hormone levels. Which design is this?
- A Prospective cohort study
- B Retrospective cohort study
- C Nested case-control study ✓
- D Case-cohort study with a simple random subcohort
Correct answer: C. Nested case-control study
Explanation
A nested case-control study is conducted entirely within a defined cohort: incident cases emerging from the cohort are identified, and controls are sampled from cohort members who remain at risk, often matched on calendar time using the risk-set approach. It permits economical assay of expensive biomarkers. A retrospective cohort would analyse outcomes for all cohort members rather than a sampled subset, and a case-cohort design draws controls from a single randomly chosen subcohort instead of matched risk sets.
Reference: Gordis Epidemiology, 6th ed.
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