Sample size and power calculations in repeated measurement analysis

Chul Ahn, John E. Overall, Scott Tonidandel

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


Controlled clinical trials in neuropsychopharmacology, as in numerous other clinical research domains, tend to employ a conventional parallel-groups design with repeated measurements. The hypothesis of primary interest in the relatively short-term, double-blind trials, concerns the difference between patterns or magnitudes of change from baseline. A simple two-stage approach to the analysis of such data involves calculation of an index or coefficient of change in stage 1 and testing the significance of difference between group means on the derived measure of change in stage 2. This article has the aim of introducing formulas and a computer program for sample size and/or power calculations for such two-stage analyses involving each of three definitions of change, with or without baseline scores entered as a covariate, in the presence of homogeneous or heterogeneous (autoregressive) patterns of correlation among the repeated measurements. Empirical adjustments of sample size for the projected dropout rates are also provided in the computer program.

Original languageEnglish (US)
Pages (from-to)121-124
Number of pages4
JournalComputer Methods and Programs in Biomedicine
Issue number2
StatePublished - Feb 2001


  • Dropouts
  • Power calculation
  • Repeated measures
  • Sample size estimate

ASJC Scopus subject areas

  • Software
  • Computer Science Applications
  • Health Informatics


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