In a prospective cohort study of 5000 smokers and 5000 non-smokers followed for 10 years, 150 smokers and 30 non-smokers develop lung cancer. The attributable risk percent (ARP) in smokers is:
- A 67%
- B 80% ✓
- C 20%
- D 75%
Correct answer: B. 80%
Explanation
Incidence in smokers = 150/5000 = 0.03; incidence in non-smokers = 30/5000 = 0.006. Attributable Risk = 0.03 − 0.006 = 0.024. ARP in exposed = (AR / Incidence in exposed) × 100 = (0.024/0.03) × 100 = 80%. This represents the proportion of lung cancer in smokers that is attributable to smoking and could theoretically be prevented if smoking were eliminated. It differs from Population Attributable Risk Percent, which considers the prevalence of exposure in the population.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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