In a cohort study, 1000 smokers and 1000 non-smokers are followed for 10 years. Lung cancer develops in 50 smokers and 5 non-smokers. The attributable risk percent (ARP) in smokers is:
- A 80%
- B 90% ✓
- C 95%
- D 50%
Correct answer: B. 90%
Explanation
Attributable Risk Percent (ARP) = (Incidence in exposed − Incidence in unexposed) / Incidence in exposed × 100. Incidence in smokers = 50/1000 = 5%; incidence in non-smokers = 5/1000 = 0.5%. ARP = (5 − 0.5)/5 × 100 = 4.5/5 × 100 = 90%. This means 90% of lung cancer in smokers is attributable to smoking. Population Attributable Risk Percent would require prevalence of smoking in the population.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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