An odds ratio calculated from a case-control study is most likely to closely approximate the relative risk that a cohort study would have produced when:
- A Controls are selected from hospitalized patients
- B Matching is performed on multiple variables
- C The disease under study is rare in the population ✓
- D Exposure prevalence exceeds 50 percent
Correct answer: C. The disease under study is rare in the population
Explanation
The odds ratio approximates the relative risk under the rare disease assumption, because when outcome frequency is low the odds of disease approximate its risk. With common outcomes, the odds ratio increasingly overestimates the relative risk. Hospital-based controls affect selection bias, and matching affects confounding control, but neither determines whether the odds ratio behaves like a risk ratio.
Reference: Gordis Epidemiology, 6th ed.
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