Panel a) shows the spectroscopic redshift distribution of our samples of CGs (black line), and LGs with N_gal ≤ 6 in two ranges of virial mass: low mass (blue line) and high mass (red line). Panel b) shows the virial mass distribution of LGs groups with N_gal ≤ 6 and 0.06 ≤ z ≤ 0.18. Panels c) and d) show the CG redshift distribution (black line), and the low-mass (blue line) and high-mass (red line) subsamples of LGs restricted to have redshift distributions similar to that of the CGs by using a Monte Carlo algorithm (see text for details).