Top panel: c − V_rms relationship for different redshifts calculated from our simulations (see discussion in the text). Middle panel: relative number of halos calculated from the number of strong lensing groups observed in each redshift bin (according to Foëx et al. 2013). Dark green histogram with tilted lines shows the results from the whole sample, light green histogram with horizontal lines those for the secure candidates. Bottom panel: c − V_rms obtained mixing, in each velocity bin, halos at different redshifts, where the relative number of halos at each redshift are equal to the observed ones, i.e., given by the fraction depicted in the middle panel. The histogram in red show the total number of halos in each velocity bin.