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In similarly designed clinical trials conducted in different regions or a multiregional trial, we sometimes observe different mean responses between trials or regions due to differences in distributions of an ethnic factor. Uesaka et al. (2003) used adjusted means for covariate, the distribution adjusted mean, to deal with such a situation. This paper examines distributional properties of the distribution adjusted mean and shows its applicability to comparison of mean responses from clinical trials where the distribution of an ethnic factor is different between regions. A real example and simulation results are shown. The results of this paper enable us to evaluate the similarity of different responses in clinical trials from different ethnic populations. [ABSTRACT FROM AUTHOR]

The objective of a multiregional bridging trial is to show the efficacy of a drug in various global regions, and at the same time to evaluate the possibility of applying the overall trial results to each region. However, to apply overall results to a specific region, the result in that region should be consistent with either the overall results or the results of other regions. This article discusses methods of sample size allocation to regions by introducing statistical criteria for consistency between regional and overall results. Specifically, three rules of sample size allocation are discussed: (1) allocating equal size to all regions, (2) minimizing total sample size, and (3) minimizing the sample size of a specific region. Some total and regional sample sizes calculated under each allocation rule are illustrated. [ABSTRACT FROM AUTHOR]