Intensity dependence of the noise envelope. SD of the log2-ratios from 40 pairs of replicate HG-U95A experiments are in black. The errors represent the variation in local SD from the 40 replicates. The intensity I = (IXIY) 1/2 measures the coordinate along the diagonal of the scatterplots, and the red lines represent the density of the variable I in arbitrary units (but the same in both panels). Note that the mode of the PM-MM lies lower than that of the PM line.
Naef et al. Genome Biology 2002 3:research0018.1 doi:10.1186/gb-2002-3-4-research0018