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Sample–Size Redetermination for Repeated Measures Studies
Author(s) -
Zucker David M.,
Denne Jonathan
Publication year - 2002
Publication title -
biometrics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.298
H-Index - 130
eISSN - 1541-0420
pISSN - 0006-341X
DOI - 10.1111/j.0006-341x.2002.00548.x
Subject(s) - sample size determination , type i and type ii errors , interim analysis , computer science , interim , range (aeronautics) , inflation (cosmology) , statistics , repeated measures design , sample (material) , clinical trial , mathematics , medicine , materials science , physics , chemistry , archaeology , pathology , chromatography , theoretical physics , composite material , history
Summary. 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.