In a case-control study, the exposure odds ratio (OR) is 2.8 with 95% CI 1.6–4.9. When the disease is rare (prevalence < 5%), the OR BEST approximates:
- A Attributable risk
- B Prevalence ratio
- C Relative risk (risk ratio) ✓
- D Incidence rate difference
Correct answer: C. Relative risk (risk ratio)
Explanation
For rare diseases (prevalence < 5–10%), the Rare Disease Assumption holds: case-control OR approximates relative risk (RR). This is because the number of cases is small relative to the total population, so the odds in each group approximate the probability. When disease is common, OR overestimates RR. This assumption justifies interpreting case-control OR as an estimate of incidence-based RR from cohort studies.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.