What does the attributable risk formula represent?

• A. Ratio of outcome incidence between exposed and unexposed
• B. Proportion of cases due to exposure
• C. Odds ratio
• D. Difference in outcome incidence between exposed and unexposed

Answer: (D)

Attributable risk is an absolute measure of how much risk in the exposed group is due to the exposure. It is calculated as the difference between the incidence in the exposed and the incidence in the unexposed. This difference represents the excess risk attributable to the exposure — the number of additional cases per population unit that could be prevented if the exposure were eliminated. It’s not a ratio; it’s a difference. For example, if 12% of the exposed develop the outcome and 8% of the unexposed do, the attributable risk is 4 percentage points, meaning 4 more cases per 100 people are attributable to the exposure.