What is the formula for Number Needed to Treat (NNT)?

The formula for Number Needed to Treat (NNT) is calculated as the inverse of the absolute risk reduction (ARR). This means that NNT represents the number of patients that need to be treated in order to prevent one additional bad outcome (such as a disease or event). The absolute risk reduction is defined as the difference in event rates between the control group and the treatment group.

When NNT is derived from the ARR, it provides a clear and clinically relevant indicator of the effectiveness of a treatment. A lower NNT indicates a more effective treatment because fewer patients need to be treated for one to benefit. This makes it a valuable metric in clinical decision-making, allowing healthcare providers to weigh the benefits of a treatment against its potential risks and costs.

The other choices do not accurately reflect the proper calculation or interpretation of NNT. For instance, simply equating NNT to the absolute risk reduction does not provide the necessary context used in the NNT formula.