From the Research
The number needed to treat (NNT) for a 2% absolute difference is 50, as calculated by taking the inverse of the absolute risk reduction (1/0.02 = 50). This means that 50 patients would need to receive the intervention for one additional patient to experience the beneficial outcome compared to the control or alternative treatment. The NNT is a valuable metric in clinical decision-making, providing a practical interpretation of treatment effectiveness 1. A lower NNT indicates a more effective intervention, while a higher NNT suggests more patients need treatment to benefit one individual. When considering implementing a treatment with an NNT of 50, clinicians should weigh this against potential harms, costs, and patient preferences, as discussed in the context of clinical relevance and significance 1. The absolute difference of 2% might represent a clinically meaningful improvement for serious outcomes like mortality or may be less compelling for milder conditions, especially if the treatment carries significant side effects or costs.
Some key points to consider when interpreting NNT include:
- The importance of defining acceptable response and adverse outcomes of interest 1
- The effect of time on NNT calculations 2
- The importance of individual baseline characteristics 1
- The need for complete reporting of NNT, including baseline risk, time horizon, and confidence intervals 3
It's also important to note that NNT should be calculated based on the results of a clinical study of good methodological quality, involving a well-defined and homogeneous group of patients, whose baseline risk is known and using a dichotomous endpoint (the event occurs or not) 4.
In clinical practice, the NNT can be a useful tool for communicating the benefits and harms of a treatment to patients, and for making informed decisions about treatment options 5. However, it's essential to consider the NNT in the context of the individual patient's circumstances, including their baseline risk, preferences, and values.