title: Sample-size redetermination for repeated measures studies.
abstract: 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.
authors.affiliation: Department of Statistics, Hebrew University, Mount Scopus, Jerusalem, Israel. mszucker@mscc.huji.ac.il
authors.forename: David M
authors.initials: DM
authors.lastname: Zucker
authors.forename: Jonathan
authors.initials: J
authors.lastname: Denne
mesh_terms: D000704:Analysis of Variance; D001699:Biometry; D002986:Clinical Trials as Topic / Q000706:statistics & numerical data*; D003627:Data Interpretation, Statistical; D006801:Humans; D016014:Linear Models; D017063:Outcome Assessment, Health Care; D011338:Probability Theory; D018401:Sample Size; D018709:Statistics, Nonparametric