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.
Original language | English |
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Pages (from-to) | 548-559 |
Number of pages | 12 |
Journal | Biometrics |
Volume | 58 |
Issue number | 3 |
DOIs | |
State | Published - Sep 2002 |
Keywords
- Clinical trial
- Internal pilot
- Longitudinal study
- Mixed linear model
- Two-stage design