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Absolute risks rather than incidence rates should be used to estimate the number needed to treat from time-to-event data

  • Ralf Bender
    Correspondence
    Corresponding author. Tel.: +49-221-35685-451; fax: +49-221-35685-10.
    Affiliations
    Department of Medical Biometry, Institute for Quality and Efficiency in Health Care, Im Mediapark 8, D–50670, Cologne, Germany

    Faculty of Medicine, University of Cologne, Joseph-Stelzmann-Str. 20, D-50931 Cologne, Germany
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  • Mandy Kromp
    Affiliations
    Department of Medical Biometry, Institute for Quality and Efficiency in Health Care, Im Mediapark 8, D–50670, Cologne, Germany
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  • Corinna Kiefer
    Affiliations
    Department of Medical Biometry, Institute for Quality and Efficiency in Health Care, Im Mediapark 8, D–50670, Cologne, Germany
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  • Sibylle Sturtz
    Affiliations
    Department of Medical Biometry, Institute for Quality and Efficiency in Health Care, Im Mediapark 8, D–50670, Cologne, Germany
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      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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