What is the formula used to calculate the number needed to harm (NNH)?

The formula to calculate the number needed to harm (NNH) is indeed represented by the equation where NNH is equal to 1 divided by the absolute risk (AR). The absolute risk refers to the difference in risk of an adverse event occurring between a group exposed to a harmful intervention and a group that is not exposed.

By using this formula, you create a measure that indicates how many patients would need to be treated for one additional patient to experience a harmful outcome. This is particularly valuable in clinical decision-making, as it helps to assess the risks associated with treatments in relation to their benefits. A lower NNH indicates that fewer people need to be exposed to the risk for one individual to experience harm, while a higher NNH suggests that the treatment is relatively safer.

The other options do not correctly represent the relationship necessary to derive NNH, as they do not adhere to the established definition and calculation for absolute risk in relation to harm.