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sometimes
informative, usually misleading
Liam Smeeth a Department of Primary Care and Population
Sciences, Royal Free and University College Medical School, University
College London, London NW3 2PF, b MRC Health Services Research Collaboration, Department of
Social Medicine, University of Bristol, Bristol BS8 2PR
Correspondence to: Professor Ebrahim
shah.ebrahim@bristol.ac.uk
| The first 150 words of the full text of this article appear below. |
The number needed to treat
the number of patients who must
be treated to prevent one adverse outcome
is a widely used
measure.
1 2
It is increasingly being calculated by
pooling absolute risk differences in trials included in
meta-analyses.
3 4
This option is available in statistical
software and the Cochrane Database of Systematic Reviews.
5 6
In this paper, we examine pooled
numbers needed to treat derived from trials and meta-analyses of
interventions to prevent cardiovascular disease. We show that a pooled
number needed to treat may be misleading because of variation in the event rates in trials, differences in the outcomes considered, effects
of secular trends on disease risk, and differences in clinical setting.
The number needed to treat should be derived by applying the relative
risk reductions from treatment which have been estimated by trials or
meta-analysis to relevant baseline risks for different types of
patients. This provides a range of
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