Size distribution of the variable segments produced in the four alignments (box plots). Each box shows the median value (middle lane), first and third quartiles (lower and upper lanes) of the size distribution. Values laying more than 1.5 times the inter-quartile value away from the bulk of all values are shown individually as dots. The width of each box is proportional to the number of VSs analyzed per alignment. On the right side, VSs shorter than 500 bp are designated by microdiversity. Abcissa: E_co, E. coli; E_B2, E. coli B2 phylogenetic group; S_au, S. aureus; S_pyo, S. pyogenes.