Blood data: 95% UCL vs. the average overall rank of the normalizing factors (Ct numbers). Each point represents one of the possible 33 = 25-1 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.