An unadjusted NNT was a moderately good predictor of health benefit.
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.


METHODS
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 <or= .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 <or=0.125 to <or=0.5 QALYs), an NNT >15 had a sensitivity of 82% to 100%. For ruling in therapies with high QALY gains (threshold >or=0.125 to >or=0.5 QALYs), an NNT <or=5 had a specificity of 77%.


CONCLUSIONS
Using NNT thresholds of <or=5 and >15 to rule in and out therapies with large QALY gains may provide general guidance regarding the magnitude of health benefit.
Department of Medicine, University of Toronto, Toronto, Ontario, Canada.
Christopher A K Y
CA
Chong
George
G
Tomlinson
Lisa
L
Chodirker
Nassi
N
Figdor
Mark
M
Uster
Gary
G
Naglie
Murray D
MD
Krahn
D003362:Cost-Benefit Analysis; D019317:Evidence-Based Medicine; D006801:Humans; D007342:Insurance Benefits; D008017:Life Expectancy; D015999:Multivariate Analysis; D011788:Quality of Life; D019057:Quality-Adjusted Life Years; D012372:ROC Curve; D018401:Sample Size; D012680:Sensitivity and Specificity; D016896:Treatment Outcome