Number needed to treat (NNT) is number of patients who need to receive an intervention of interest (compared with an alternative) order for one unit of health outcome to be gained – or one unit to be prevented in the case of an adverse outcome. For example an NNT of 50 to prevent a myocardial infarction (MI) means that 50 patients need to be treated for 1 MI to be prevented –or, for every 1,000 patients treated 20 MIs are expected to be prevented. NNT is numerically equivalent to the reciprocal of the absolute risk reduction (1/ARR). NNTs have been popularised as a central concept in evidence based medicine (clinical epidemiology), as a simple way of communicating the results of clinical trials. They requires a defined endpoint (maybe less good for chronic, progressive conditions) and are time-specific: in the case above the duration of treatment and time period over which MIs may be prevented need to be specified. The degree of patient benefit associated with different endpoints may vary. As similar NNTs may be generated with different combinations of underlying risk and risk reductions, they should not be used directly in meta-analysis.

How to cite: Number Needed to Treat [online]. (2016). York; York Health Economics Consortium; 2016.

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