Breast tumor data: 95% UCL vs. the average overall rank of the normalizing factors. Each point represents one of the possible 63 = 26-1 gene subsets. Different colors are used for the subsets with different numbers of genes included. The x-coordinate is the average overall rank of the corresponding normalizing factor variance. The y-coordinate is the upper 95% confidence limit (95% UCL) for the standard deviation of the log normalizing factor. The red dot, which is closest to the lower left corner, represents the optimal (in the sense of criteria A and C) combination of two genes, ACTB and SF3A1.