Mass accretion rate vs. period. Relevant correlation parameters are given for all classes. Linear fit lines to the UX and nSW classes (dashed) as well as the whole sample (dotted) are plotted. They appear curved because the x-axis is rendered in log to avoid crowding of data at short periods. V426 Oph is highlighted with a square box (see last paragraph of Sect. 6.2 for details).