Survivor Function Estimators Under Group Sequential Monitoring Based on the Logrank Statistic |
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Authors: | Gorfine Malka |
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Affiliation: | (1) Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. N. MP1002, P.O. Box 19024, Seattle, WA 98109-1024, USA |
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Abstract: | 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. |
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Keywords: | group sequential test secondary parameter Kaplan-Meier curve logrank test local alternatives |
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