For a beneficial intervention reducing an adverse-event risk from to over a stated follow-up period, the number needed to treat is the reciprocal of the absolute risk reduction. Its clinical interpretation requires the population, outcome, horizon and comparison to be specified. Invert confidence limits for the risk difference in reversed order if both are positive. If the interval includes zero, the transformed confidence set is unbounded and may include both benefit and harm, rather than being one ordinary finite interval.
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The Number Needed to Treat (NNT) is a statistical measure used in healthcare to estimate the effectiveness of a treatment. It indicates the number of patients that need to be treated with a particular intervention in order for one patient to benefit from that treatment compared to a control group (usually receiving a placebo or standard care). The NNT is calculated from the absolute risk reduction (ARR), which is the difference in the event rate (e.g.