Virial concentration versus non-parametric R₉₀/R₅₀. The colours represent median values of the residuals of the NFW-fits. The lens sample (circles) shows mostly large negative residuals (magenta), whereas the EAGLE sample (squares) shows small positive residuals (green). The X- and Y-axis histograms show two populations: kernel densities for the EAGLE sample (solid black line) and the lens sample (dashed grey line). A two-sample KS test for c_vir and R₉₀/R₅₀ for a significance level of α = 0.001 indicated that the two samples are drawn from different populations.