An unadjusted NNT was a moderately good predictor of health benefit

Chong, Christopher A.K.Y.; Tomlinson, George; Chodirker, Lisa; Figdor, Nassi; Uster, Mark; Naglie, Gary; Krahn, Murray D.

doi:10.1016/j.jclinepi.2005.08.005

« Previous Next »Journal of Clinical Epidemiology
Volume 59, Issue 3 , Pages 224-233, March 2006

An unadjusted NNT was a moderately good predictor of health benefit

Christopher A.K.Y. Chong
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
George Tomlinson
- Department of Biostatistics, University of Toronto, Ontario, Canada
- Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada
Lisa Chodirker
- Department of Health Policy, Management, and Evaluation, University of Toronto, Toronto, Ontario, Canada
Nassi Figdor
- Department of Health Policy, Management, and Evaluation, University of Toronto, Toronto, Ontario, Canada
Mark Uster
- Department of Health Policy, Management, and Evaluation, University of Toronto, Toronto, Ontario, Canada
Gary Naglie
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
- Department of Biostatistics, University of Toronto, Ontario, Canada
- Department of Health Policy, Management, and Evaluation, University of Toronto, Toronto, Ontario, Canada
- University Health Network, Toronto General Hospital, 200 Elizabeth Street, ES-14 207, Toronto, Ontario M5G 2C4, Canada
- Geriatrics Program, Toronto Rehabilitation Institute, University of Toronto, Toronto, Ontario, Canada
Murray D. Krahn
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
- Department of Biostatistics, University of Toronto, Ontario, Canada
- Department of Health Policy, Management, and Evaluation, University of Toronto, Toronto, Ontario, Canada
- University Health Network, Toronto General Hospital, 200 Elizabeth Street, ES-14 207, Toronto, Ontario M5G 2C4, Canada
- Geriatrics Program, Toronto Rehabilitation Institute, University of Toronto, Toronto, Ontario, Canada
- Corresponding author. Tel.: 416-340-4155; fax: 416-595-5826.

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.

Keywords: Decision analysis, Cost-effectiveness analysis, Evidence-based medicine, Number needed to treat, Quality-adjusted life years