Comparison between the input halo mass M₂₀₀ and the group mass proxy based on the total luminosity scaled through the scaling relation of Popesso et al. (2005) for the three optically selected galaxy group samples: R11 (left panel), T17 (central panel) and Y05 (right panel. The solid line indicates the 1:1 relation. The green symbols indicate in all panels the mean M₂₀₀ obtained in bins of 0.3 dex width of M_lum, whilst the error bars indicate the dispersion. The bottom panel shows the residuals Δ = log(M_lum)−log(M₂₀₀) of the individual points and the mean values (green symbols) for the three group samples.