A prospective cohort study follows 5000 smokers and 5000 non-smokers for 10 years. Among smokers 200 develop lung cancer (incidence rate 40/1000); among non-smokers 10 develop lung cancer (incidence rate 2/1000). The Attributable Risk Percent (ARP) among the exposed is:
- A 95% ✓
- B 38/1000
- C 20
- D 5%
Correct answer: A. 95%
Explanation
Attributable Risk Percent (Etiologic fraction) among the exposed = (RR-1)/RR × 100 = (20-1)/20 × 100 = 95%. Alternatively, AR = 40 - 2 = 38/1000; ARP = 38/40 × 100 = 95%. This means 95% of lung cancer in smokers is attributable to smoking. Option B is the Attributable Risk (absolute excess risk), not the percentage. Option C is the Relative Risk (RR = 40/2 = 20). Option D is the reverse fraction.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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