Absolute Risk Reduction
The actual numerical difference in event rates between the treatment and control groups. If the event rate is 10% with placebo and 8% with treatment, the absolute risk reduction is 2 percentage points. This measure provides more practical context than relative risk reduction.
Technical Context
ARR = control event rate - treatment event rate. ARR directly tells you what proportion of patients benefit from treatment and is the basis for NNT calculation. ARR is population-dependent — the same RRR produces different ARRs in high-risk vs low-risk populations. For GLP-1 RA trials, the ARR for weight achievement thresholds (≥5%, ≥10%, ≥15% weight loss) can be large: if 85% of treated patients vs 30% of placebo patients achieve ≥5% weight loss, the ARR is 55% (NNT ≈ 2). This contrasts with the smaller ARR for preventing cardiovascular events (~1-2% over 3-5 years). ARR contextualises clinical benefit more directly than RRR for individual patient decision-making.