What is attributable risk?

• A. The proportion of disease in the population attributed to exposure.
• B. The excess risk in exposed individuals compared to unexposed.
• C. The overall risk in the population.
• D. The risk reduction from an intervention.

Answer: (B)

Attributable risk, also called the risk difference, is the extra risk of disease seen in those who are exposed compared with those who are not exposed. It is calculated as the risk in the exposed group minus the risk in the unexposed group. This quantity tells you how many additional cases per person (or per 100,000 people) in the exposed group can be attributed to the exposure and therefore how many cases could be prevented if the exposure were eliminated among the exposed. It is a within-group measure, focusing on the excess risk due to the exposure, and is different from the overall risk in the population (which looks at everyone) and from relative risk (which is a ratio of risks) or from the impact of an intervention (which assesses risk reduction due to an intervention rather than simply the exposure itself). For example, if 20% of the exposed develop the disease and 10% of the unexposed do, the attributable risk is 10 percentage points (0.20 minus 0.10), meaning 10 extra cases per 100 exposed are attributable to the exposure.