The group exposed to treatment (left) has the risk of an adverse outcome (black) reduced by 50% <unk>  = 0.5) compared to the unexposed group (right). In epidemiology, the<unk>  <unk>  or efficacy is the<unk>  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, the term<unk>  risk increase (RRI) is used, and computed as . If the direction of risk change is not assumed, the term<unk>  effect is used and computed as .
Relative risk reduction
Risk difference
Indicative limit value
Number needed to treat
Minimal important difference
Absolute threshold
Number needed to harm
Odds ratio