Calculate absolute risk reduction and the number needed to treat.
Absolute risk reduction is the difference in percentage points, and its reciprocal is the number needed to treat. NNT is the most decision-relevant measure because it accounts for baseline risk. An NNT of 100 means 99 patients receive treatment, and any side effects, without benefit — which is the trade-off relative measures conceal.
Absolute Risk Reduction
ARR = control rate − treatment rate; NNT = 1 ÷ ARR
ARR = control rate − treatment rate; NNT = 1 ÷ ARR Absolute risk reduction is the difference in percentage points, and its reciprocal is the number needed to treat. NNT is the most decision-relevant measure because it accounts for baseline risk.
An NNT of 100 means 99 patients receive treatment, and any side effects, without benefit — which is the trade-off relative measures conceal.
This calculator takes 3 inputs: Control event rate, Treatment event rate, Population treated. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.