A researcher wants to test whether serum vitamin D levels measured years earlier predict subsequent development of type 2 diabetes. She has a pre-existing cohort of 20,000 adults with banked baseline blood samples. To save costs, she identifies all 400 incident diabetic cases from the cohort and compares their baseline vitamin D levels with those of a sample of 800 non-diabetic members of the same cohort. Which study design has she employed?
- A Classic case-control study
- B Nested case-control study ✓
- C Retrospective cohort study
- D Case-cohort study
Correct answer: B. Nested case-control study
Explanation
A nested (case-control within a cohort) study selects cases arising inside an identified cohort and draws controls from the risk set of the same cohort, allowing use of banked specimens at far lower cost than assaying the full cohort. A classic case-control draws cases and controls from the general source population without a defined cohort. A retrospective cohort would analyse the entire exposed and unexposed groups, which is exactly what the costly assay makes impractical here.
Reference: Gordis Epidemiology, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.