Number Needed to Treat (NNT)

Number Needed to Treat (NNT) is the number of patients who need to receive an intervention (compared with an alternative) for one additional unit of a health outcome to be achieved or one adverse outcome to be prevented. For example, an NNT of 50 to prevent a myocardial infarction (MI) means that 50 patients need to be treated to prevent one MI. This implies that treating 1,000 patients would prevent approximately 20 MIs.

Key aspects of NNT include:

– Calculation: NNT is the reciprocal of the absolute risk reduction (ARR). For example, if the ARR is 0.02 (or 2%), the NNT would be 1 / 0.02 = 50.

– Communication: NNTs are widely used in evidence-based medicine as a straightforward way to convey the results of clinical trials.

– Defined Endpoints: NNT requires a clearly defined endpoint, making it less suitable for chronic, progressive conditions.

– Time-Specific: The duration of treatment and the time period over which outcomes are measured must be specified for NNT to be meaningful.

– Patient Benefit: The degree of benefit can vary depending on the specific endpoints being considered.

– Limitations: Similar NNTs can result from different combinations of underlying risk and risk reductions, so they should not be used directly in meta-analysis.

NNT provides a simple, intuitive measure for clinicians and policymakers to understand the effectiveness of an intervention, helping to guide treatment decisions and healthcare resource allocation.

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