Distribution of features in the two-dimensional space of log2(variance) and average expression. Data for two different pre-processing methods: MAS5 – left panel and RMA – right panel from data set GSE6011 (see Table1) consisting of 37 samples. Blue line provides the mean E[μ |log2(vT)] under fixed variance and red line the mean E[log2(vT) | μ] under fixed average expression. The following colour scheme is used for plotting 2D distribution: green – minimum (0), yellow – maximum. Bright yellow spots therefore indicate high density location of features. On each panel, marginalized distribution of features over variance is shown on the left side and marginalized distribution over average expression is shown at the bottom of the panel.