Sample-size redetermination for repeated measures studies

David M. Zucker*, Jonathan Denne

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


Clinical trialists recently have shown interest in two-stage procedures for updating the sample-size calculation at an interim point in a trial. Because many clinical trials involve repeated measures designs, it is desirable to have available practical two-stage procedures for such designs. Shih and Gould (1995, Statistics in Medicine 14, 2239-2248) discuss sample-size redetermination for repeated measures studies but under a highly simplified setup. We develop two-stage procedures under the general mixed linear model, allowing for dropouts and missed visits. We present a range of procedures and compare their Type I error and power by simulation. We find that, in general, the achieved power is brought considerably closer to the required level without inflating the Type I error rate. We also derive an inflation factor that ensures the power requirement is more closely met.

Original languageAmerican English
Pages (from-to)548-559
Number of pages12
Issue number3
StatePublished - Sep 2002


  • Clinical trial
  • Internal pilot
  • Longitudinal study
  • Mixed linear model
  • Two-stage design


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