A researcher has a biobank of serum samples collected from 20,000 adults at baseline, stored for 15 years. Of these, 130 have now developed stomach cancer. She selects 4 cancer-free controls per case, matched on age and sex, and assays H. pylori antibodies only in these samples rather than in all 20,000. Which statement best describes this design?
- A It is a case-cohort design because controls come from the full cohort
- B Exposure was measured before disease onset, avoiding recall bias, at far lower cost than analysing the whole cohort ✓
- C It is a retrospective cohort because the outcome has already occurred
- D Temporality cannot be established because exposure measurement followed cohort entry
Correct answer: B. Exposure was measured before disease onset, avoiding recall bias, at far lower cost than analysing the whole cohort
Explanation
This is a nested case-control study: cases arise from within a defined cohort and controls are sampled from the risk set, while the pre-existing banked specimens ensure exposure status was recorded before disease developed. It retains much of the temporal strength of a cohort study at a fraction of laboratory cost. Option A describes a different control-sampling scheme, and temporality is preserved precisely because sera predate the outcome.
Reference: Rothman, Greenland and Lash, Modern Epidemiology, 3rd ed.
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Written and medically reviewed by the StethoPrep medical team.