title: The use of numbers needed to treat derived from systematic reviews and meta-analysis. Caveats and pitfalls.
abstract: Numbers needed to treat (NNTs) may be used to present the effects of treatment and are the reciprocal of the absolute difference between treatment and control groups in a randomized controlled trial. NNTs are sensitive to factors that change the baseline risk of trial participants: the outcome considered; characteristics of patients; secular trends in incidence and case-fatality; and clinical setting. NNTs derived from pooled absolute risk differences in meta-analyses are commonly presented and easily calculated by meta-analytic software but may be seriously misleading because of heterogeneity between trials included in meta-analyses. Meaningful NNTs are obtained by applying the pooled relative risk reductions calculated from meta-analyses or individual trials to the baseline risk relevant to specific patient groups. This process will give a range of NNTs depending on whether patients are at high, low, or intermediate levels of risk, rather than a potentially misleading single number.
authors.affiliation: University of Bristol.
authors.forename: S
authors.initials: S
authors.lastname: Ebrahim
mesh_terms: D002986:Clinical Trials as Topic; D019317:Evidence-Based Medicine; D006801:Humans; D015201:Meta-Analysis as Topic; D008722:Methods; D016032:Randomized Controlled Trials as Topic; D018570:Risk Assessment; D016896:Treatment Outcome