Flexible stopping boundaries when changing primary endpoints after unblinded interim analyses

Liddy M. Chen, Joseph G. Ibrahim, Haitao Chu

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


It has been widely recognized that interim analyses of accumulating data in a clinical trial can inflate type I error. Different methods, from group sequential boundaries to flexible alpha spending functions, have been developed to control the overall type I error at prespecified level. These methods mainly apply to testing the same endpoint in multiple interim analyses. In this article, we consider a group sequential design with preplanned endpoint switching after unblinded interim analyses. We extend the alpha spending function method to group sequential stopping boundaries when the parameters can be different between interim, or between interim and final analyses.

Original languageEnglish (US)
Pages (from-to)817-833
Number of pages17
JournalJournal of Biopharmaceutical Statistics
Issue number4
StatePublished - Jul 4 2014

Bibliographical note

Funding Information:
H. Chu is supported in part by the US NCI 1P01CA142538, NCI 2P30CA077598, and U54-MD008620.


  • Alpha spending function
  • Group sequential trials
  • Interim analyses
  • Stopping boundaries
  • Switching endpoints


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