The use of numbers needed to treat derived from systematic reviews and meta-analysis. Caveats and pitfalls.
Ebrahim, S;
(2001)
The use of numbers needed to treat derived from systematic reviews and meta-analysis. Caveats and pitfalls.
Evaluation & the health professions, 24 (2).
pp. 152-164.
ISSN 0163-2787
DOI: https://doi.org/10.1177/01632780122034858
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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.