Journal
STATISTICS IN MEDICINE
Volume 23, Issue 18, Pages 2781-2798Publisher
WILEY
DOI: 10.1002/sim.1877
Keywords
sample size; non-inferiority; equivalence; active control; adaptive design
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Funding
- NCI NIH HHS [2P30 CA 72720-04] Funding Source: Medline
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In active controlled trials without a placebo arm, there are usually two study objectives: to test a superiority hypothesis that the experimental treatment is more effective than the active control therapy, and to test a non-inferiority hypothesis that the experimental treatment is therapeutically no worse than the active control within a defined margin. For a two-stage adaptive design, it is not necessary to give a fixed sample size calculation at the planning stage of the study when treatment effect information is often insufficient. Instead, decision and estimation of the design specifications can be made more reliably after the first stage when interim results are available. We propose the use of conditional power approach to determine the sample size and critical values for testing the superiority and non-inferiority hypotheses for the second stage based on the observed result of the first stage. The proposed adaptive procedure preserves the overall type 1 error rate for both superiority and non-inferiority, and has the flexibility of early termination of the study (for futility or efficacy) or extending the study by appropriate sample size. Copyright (C) 2004 John Wiley Sons, Ltd.
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