Effect of normalization method on variation of miRNA expression. Each point represents the mean standard deviation from all miRNAs (All miRNAs; n = 377) or the restricted set of miRNAs (Restricted miRNAs; n = 19) on the TaqMan array, but calculated separately across all samples within a given group (Sample Origin). The restricted set of miRNAs is the core set of miRNAs detected across all samples in all titrations. Note that all data were normalized together, and this is most important for methods that share information across samples. NormFinder was parameterized to use the sample origin for grouping. GeNorm, NormFinder, and CCR results are based on the selection of two miRNAs as normalizers.