Abstract
Objective
To illustrate basic issues that have to be taken into account when study results are
presented by means of the number needed to treat (NNT).
Study Design and Setting
This article presents an overview of common problems related to the NNT with corresponding
explanations.
Results
Without stating the direction of the effect, the alternative treatment, the treatment
period, and the follow-up period, information in terms of NNTs is uninterpretable.
The naive use of person-time data for the calculation of NNTs is frequently inappropriate.
Rounding NNTs to the next upward integer may obscure differences among therapies.
Conclusions
The basic information about which treatments are compared, the treatment period, the
follow-up period, and the direction of the effect should be given when study results
are presented in terms of NNTs. Adequate methods should be used for point and interval
estimation of NNTs. Unnecessary rounding of NNTs should be avoided. In more complicated
situations of confounding or varying follow-up times, the use of more sophisticated
methods is required with increasing potential for misinterpretation.
Keywords
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Article info
Publication history
Published online: November 02, 2009
Accepted:
August 3,
2009
Identification
Copyright
© 2010 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
