Approximations in a group sequential test with unequal group sizes

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Our concern in this paper is a group sequential test design for which the sample sizes between interim analyses are not identical. First, we consider a repeated significance test for comparing two treatments in a clinical trial, and study asymptotic properties of the test statistic. Using the arguments developed by Siegmund (1985, Chapters 8 and 9), we then obtain approximations for the overall significance level of the test and for the error level at each interim analysis. Simulation studies are performed to assess the accuracy of the approximations and the robustness of the approximations are examined using numerical examples.

Original languageEnglish (US)
Pages (from-to)915-924
Number of pages10
JournalCommunications in Statistics - Simulation and Computation
Issue number4
StatePublished - Jan 1 1994


  • approximate significance level
  • approximate use function
  • boundary crossing probability

ASJC Scopus subject areas

  • Statistics and Probability
  • Modeling and Simulation


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