Lifetime Data Analysis

, Volume 9, Issue 2, pp 175–193 | Cite as

Survivor Function Estimators Under Group Sequential Monitoring Based on the Logrank Statistic

  • Malka Gorfine


In this paper we investigate a group sequential analysis of censored survival data with staggered entry, in which the trial is monitored using the logrank test while comparisons of treatment and control Kaplan-Meier curves at various time points are performed at the end of the trial. We concentrate on two-sample tests under local alternatives. We describe the relationship of the asymptotic bias of Kaplan-Meier curves between the two groups. We show that even if the asymptotic bias of the Kaplan-Meier curve is negligible relative to the true survival, this is not the case for the difference between the curves of the two arms of the trial. A corrected estimator for the difference between the survival curves is presented and by simulations we show that the corrected estimator reduced the bias dramatically and has a smaller variance. The methods of estimation are applied to the Beta-Blocker Heart Attack Trial (1982), a well-known group sequential trial.

group sequential test secondary parameter Kaplan-Meier curve logrank test local alternatives 


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Copyright information

© Kluwer Academic Publishers 2003

Authors and Affiliations

  • Malka Gorfine
    • 1
  1. 1.Fred Hutchinson Cancer Research CenterSeattleUSA

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