An under-used yet easily understood statistic: the number needed to treat (NNT)

Objectives Interpretation of the research literature can be difficult, yet it is essential in order for physiotherapists to convey the details of risks and benefits associated with therapeutic interventions to patients. The number needed to treat (NNT) statistic is one such statistic that is easily interpretable. Using several examples from the physiotherapy literature representing a range of conditions, this article demonstrates how to convert more commonly used statistics into the NNT statistic. The purpose of this is to show how the NNT can help clinicians to converse with patients to convey details about the likelihood of benefit with treatment and/or the likelihood of risk, in order that a decision may be made with respect to therapy. Design The Australian Physiotherapy Evidence Database (PEDro) was searched in order to locate a selection of physiotherapy research articles that reported various dichotomous outcomes that could be converted to the NNT statistic for the purpose of this analysis. Results The NNT statistic for nine studies with a PEDro score >= 6 was calculated using the Internet-based downloadable spreadsheet on the PEDro website. For six studies, the NNT point estimates ranged from 2 to 4 (95% confidence interval 1-10). One study had a NNT of 8, while two other studies produced number needed to harm values. Conclusion The NNT can be calculated quickly and efficiently using Internet-based calculators and/or other decision-making tools, and may be an alternative that provides readily interpretable information to assist in conveying the likely benefits (and/or risks) of treatment to patients. (c) 2006 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved.