An unadjusted NNT was a moderately good predictor of health benefit

Background and ObjectiveWhether the number needed to treat (NNT) is sufficiently precise to use in clinical practice remains unclear. We compared unadjusted NNTs to quality-adjusted life years (QALYs) gained, a more comprehensive measures of health benefit.Study Design and SettingFrom a subset (n = 65) of a dataset of 228 cost-effectiveness analyses, we compared how well NNTs predicted clinically important QALY gains using correlation analysis, multivariable models and receiver-operator curve (ROC) analysis.ResultsNNT was inversely correlated with QALY gains (P < .001); this relationship was affected by quality of life and life-expectancy gains of treatment (P ≤ .04). The NNT is a moderately accurate predictor of treatments that provide large health benefits (area under ROC 0.74–0.81). For ruling out therapies with low QALY gains (threshold ≤0.125 to ≤0.5 QALYs), an NNT >15 had a sensitivity of 82% to 100%. For ruling in therapies with high QALY gains (threshold ≥0.125 to ≥0.5 QALYs), an NNT ≤5 had a specificity of 77%.ConclusionUsing NNT thresholds of ≤5 and >15 to rule in and out therapies with large QALY gains may provide general guidance regarding the magnitude of health benefit.