The inter-gene correlation within GO categories is consistent across experiments and platforms. Mean correlation among genes in GO categories (a,b) and KEGG pathways (c,d) on two human (a,c) and two mouse (b,d) microarray platforms. The correlation of all transcripts with all transcripts on each platform is shown in red. Spearman correlations of the correlations are in upper right. Crosses represent +/- 1 standard error on each axis.