The weighting function used in PADOG. The left panel shows the distribution of gene frequencies across the set of KEGG non-metabolic pathways. About 42% of genes that appear in at least one pathway appear also in other pathways. Gene frequencies over the 99th percentile of frequencies, i.e. over 20, were replaced with the value 20. The right panel shows the gene weight (Eq. 1) as a function of gene frequency.