How do you calculate NNH?

NNH, or Number Needed to Harm, is calculated by taking the inverse of the absolute risk increase (ARI) associated with a treatment or intervention. First, determine the event rates in both the treatment and control groups, then calculate the ARI by subtracting the control event rate from the treatment event rate. Finally, NNH is calculated as ( \text{NNH} = \frac{1}{\text{ARI}} ). This value represents the average number of patients who need to be treated for one additional patient to experience harm.