Relative risk reduction


In epidemiology, the relative risk reduction or efficacy is the relative decrease in the risk of an adverse event in the exposed group compared to an unexposed group. It is computed as, where is the incidence in the exposed group, and is the incidence in the unexposed group. If the risk of an adverse event is increased by the exposure rather than decreased, term relative risk increase is used, and computed as. If the direction of risk change is not assumed, a term relative effect is used and computed as.

Numerical examples

Risk reduction

Risk increase