Box plot of concentrations (top panel) and virial masses (bottom panel) plotted against γ_GNFW for the four lenses J0037, J0044, J0946, and J2343. Mean values and standard errors are shown as black dots with error bars in addition to the box plots showing the interquartile range (25–75%) and whiskers at the 90% confidence interval. The small vertical numbers show how many of the original 10 000 realisations produced viable fits.