Sample-size redetermination for repeated measures studies |
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Authors: | Zucker David M Denne Jonathan |
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Institution: | Department of Statistics, Hebrew University, Mount Scopus, Jerusalem, Israel. mszucker@mscc.huji.ac.il |
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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. |
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Keywords: | Clinical trial Internal pilot Longitudinal study Mixed linear model Two-stage design |
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