Adaptive sample size calculations in group sequential trials

Biometrics. 1999 Dec;55(4):1286-90. doi: 10.1111/j.0006-341x.1999.01286.x.


A method for group sequential trials that is based on the inverse normal method for combining the results of the separate stages is proposed. Without exaggerating the Type I error rate, this method enables data-driven sample size reassessments during the course of the study. It uses the stopping boundaries of the classical group sequential tests. Furthermore, exact test procedures may be derived for a wide range of applications. The procedure is compared with the classical designs in terms of power and expected sample size.

Publication types

  • Comparative Study

MeSH terms

  • Acne Vulgaris / drug therapy
  • Acne Vulgaris / microbiology
  • Biometry*
  • Chloramphenicol / administration & dosage
  • Clinical Trials as Topic / statistics & numerical data*
  • Colony Count, Microbial
  • Confidence Intervals
  • Humans
  • Models, Statistical
  • Randomized Controlled Trials as Topic / statistics & numerical data
  • Sample Size


  • Chloramphenicol