Abstract
Background
When estimating the number needed to treat (NNT) from randomized controlled trials
(RCTs) with time-to-event outcomes, varying follow-up times have to be considered.
Two methods have been proposed, namely (1) inverting risk differences estimated by
survival time methods (RD approach) and (2) inverting incidence differences (ID approach).
Study Design and Setting
A simulation study was conducted to compare the RD and the ID approaches regarding
bias and coverage probability (CP) considering various distributions, baseline risks,
effect sizes, and sample sizes. Additionally, the two approaches were compared by
using two real data examples.
Results
The RD approach showed good estimation and coverage properties with only a few exceptions
in the case of small sample sizes and small effect sizes. The ID approach showed considerable
bias and low CPs in most of the considered data situations.
Conclusions
Absolute risks estimated by means of survival time methods rather than incidence rates
should be used to estimate NNTs in RCTs with time-to-event outcomes.
Keywords
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Article info
Publication history
Published online: June 24, 2013
Accepted:
January 17,
2013
Identification
Copyright
© 2013 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
