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Combined test versus logrank/Cox test in 50 randomised trials.

Patrick Royston1, Babak Choodari-Oskooei2, Mahesh K B Parmar2

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The proportional hazards assumption is often violated in randomized controlled trials (RCTs), reducing statistical power. A combined test offers a more robust alternative to the Cox test for time-to-event analysis in clinical trials.

Keywords:
Combined testCox testHazard ratioLogrank testNon-proportional hazardsRandomised controlled trialsRobustnessTime-to-event outcome

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Area of Science:

  • Biostatistics
  • Clinical Trials Methodology

Background:

  • Logrank test and Cox proportional hazards model are standard for time-to-event outcomes in randomized controlled trials (RCTs).
  • Sample size and power calculations typically assume proportional hazards (PH), where the hazard ratio remains constant.
  • Failure of the PH assumption can significantly reduce the power of standard statistical tests.

Purpose of the Study:

  • To assess the frequency and impact of non-proportional hazards (non-PH) in published phase 3 clinical trials.
  • To compare the performance of the standard logrank/Cox test with a recently proposed combined test under non-PH conditions.

Main Methods:

  • Systematic search of four leading medical journals for phase 3 clinical trials with time-to-event outcomes.
  • Digitization of Kaplan-Meier curves to reconstruct individual patient-level data.
  • Testing for non-PH and comparing results from the logrank/Cox test and the combined test.

Main Results:

  • The PH assumption was checked in only 28% of the 50 included trials.
  • Evidence of non-PH was detected in 31% of comparisons.
  • The combined test showed higher significance rates (55%) compared to the Cox test (49%), with interpretation changes in 4 out of 5 discordant trials.
  • Non-PH was often characterized by early treatment effects that diminished over time.

Conclusions:

  • Non-PH is likely under-identified in RCTs but may be prevalent.
  • The combined test demonstrated superior performance over the Cox test in this reanalysis.
  • The combined test represents a more robust approach for the design and analysis of clinical trials with time-to-event data.