Understanding Absolute Risk Reduction

ARR is the absolute risk of events in the control group (ARC) minus the absolute risk of events in the exposed or treatment group (ART): ARR = ARC–ART. The negative of the risk difference. It is also the proportion of untreated persons who experience an adverse event minus the proportion of treated persons who experience this event.

The ARR varies with the underlying risk of an event; e.g., it becomes smaller when event rates are low.

The ARR is one measure of the strength of an association.