Number Needed to Treat: A Statistic Relevant for Physical Therapists

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Abstract
The number needed to treat (NNT) is a method of reporting outcomes from clinical trials.1 Treatment efficacy is determined by evaluating the outcome of one treatment relative to another treatment or to a control group when the only difference between the groups is the intervention of interest. The NNT can also be used to express the size of the outcome of one treatment relative to another. The NNT is expressed in terms designed to help decide whether the intervention might be valuable in clinical practice: the number of patients who need to be treated before a therapist can be sure that one patient improved who would not have improved without the intervention. For example, when comparing treatment X and treatment Y, an NNT score of 5 for treatment X indicates that, on average, after treating 5 patients, treatment X will have achieved one more positive outcome than if treatment Y had been used. The NNT does not tell the clinician which of those 5 patients will respond, only that 1 patient is likely to do so.