Upper panel: Low-number bias for the eight clusters selected in this paper compared to the related analytical curve with the best-fit ρ = −0.788. To illustrate the statistical uncertainty without overcrowding the graph, we only show the A2199 one-sigma error band forreference. Lower panel: Residuals, Δ, between the data points and the analytical curves. In the legend, we use N_t = N_tot, v_r = v_rot, and σ calculated as the standard deviation of the full set of galaxies (this is what ultimately causes the difference between the values of v_r/σ reported here and the v_rot/σ_fit in Table 2, where σ_fit is extracted from the Gaussian fit of the redshift distribution). The case of N = 10 was excluded from the analysis, as undesired additional systematic effects are expected to appear with such a small number of galaxies.