In a 10-year prospective cohort study, the incidence of myocardial infarction (MI) in smokers is 12 per 1000 person-years and in non-smokers is 4 per 1000 person-years. The population prevalence of smoking is 30%. The Population Attributable Risk Percent (PAR%) for smoking in MI is closest to:
- A 33%
- B 25%
- C 40% ✓
- D 20%
Correct answer: C. 40%
Explanation
PAR% = (I_pop − I_unexposed) / I_pop × 100. I_pop = (0.30 × 12) + (0.70 × 4) = 3.6 + 2.8 = 6.4 per 1000 person-years. PAR% = (6.4 − 4.0) / 6.4 × 100 = 2.4/6.4 × 100 = 37.5%. This is closest to 40% among the given choices. Alternatively using the Levin formula: PAR% = Pe(RR−1) / [1 + Pe(RR−1)] × 100 = 0.30 × 2 / (1 + 0.60) × 100 = 37.5%. PAR% reflects both the strength of association (RR = 3) and the population exposure prevalence (30%); it represents the proportion of MI burden theoretically preventable if smoking were eliminated.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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