An unadjusted NNT was a moderately good predictor of health benefit
Accepted 8 August 2005.
Abstract
Background and Objective
Whether 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 Setting
From 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.
Results
NNT 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%.
Conclusion
Using 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.
ABSTRACT