Effects of coexpression on different null hypotheses. Expression profiles, over the 97 samples in van 't Veer et al. , of the 12 most highly ranked genes in the "M phase" category (left) and 13 most highly ranked genes in the "carboxylic acid metabolism" category (right), respectively. Some genes were inverted since the ranking was based on absolute correlation values to metastasis class. The metastasis free samples are to the left of the vertical line, and within each metastasis class, samples are ordered in increasing average expression of the examined genes. The expressions of each gene was normalized to zero average across samples. The narrower band of expressions in the left figure illustrates the higher Pearson correlation of M phase genes. Average absolute Pearson correlation between gene expressions was 0.74, with standard deviation of 0.16, for the M phase genes, and 0.44, with standard deviation of 0.27, for carboxylic acid metabolism genes.