In a cohort study on 500 exposed and 500 unexposed individuals followed for 5 years, 50 exposed developed disease versus 20 unexposed. The Attributable Risk (AR) is:
- A 0.06 per person ✓
- B 2.5
- C 0.04 per person
- D 60%
Correct answer: A. 0.06 per person
Explanation
Attributable Risk = Incidence in exposed – Incidence in unexposed = 50/500 – 20/500 = 0.10 – 0.04 = 0.06 per person per 5 years. This is the excess risk attributable to exposure. Option B (2.5) represents the Relative Risk (0.10/0.04). Option C would be wrong arithmetic; Option D is the Attributable Risk Percent, not AR.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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