epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decisions and evide ...

, the relative risk reduction (RRR) or efficacy is the relative decrease in the

risk In simple terms, risk is the possibility of something bad happening. Risk involves uncertainty about the effects/implications of an activity with respect to something that humans value (such as health, well-being, wealth, property or the environm ...

of an adverse event in the exposed group compared to an unexposed group. It is computed as

(I_u - I_e) / I_u

, where

I_e

is the incidence in the exposed group, and

I_u

is the incidence in the unexposed group. If the risk of an adverse event is increased by the exposure rather than decreased, the term relative risk increase (RRI) is used, and it is computed as

(I_e - I_u)/I_u

. If the direction of risk change is not assumed, the term relative effect is used, and it is computed in the same way as relative risk increase.

Numerical examples

Risk reduction

Risk increase

See also

References