In a prospective cohort study comparing smokers (n=2,000) and non-smokers (n=5,000) over 10 years, 80 smokers and 40 non-smokers developed lung cancer. What is the population attributable risk percent (PAR%) assuming smokers constitute 20% of the general population? (Incidence in smokers = 40/1000; Incidence in non-smokers = 8/1000; Overall population incidence = 14.4/1000)

• A 44.4% ✓
• B 80%
• C 55.6%
• D 20%

Explanation

Population Attributable Risk % = (Incidence in total population - Incidence in unexposed) / Incidence in total population × 100 = (14.4 - 8) / 14.4 × 100 = 6.4/14.4 × 100 ≈ 44.4%. This measures the proportion of disease in the entire population attributable to the exposure. It differs from attributable risk in exposed (which = 40-8=32/1000 = 80% of smokers' lung cancer is attributable to smoking), and is more relevant for public health policy decisions.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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