Black points: stellar mass density concentration for the clusters used in this study, split in two redshift bins. Purple: K-band luminosity density concentration in CNOC1 from Muzzin et al. (2007). Red: stellar mass density concentration in GCLASS from vdB14. The horizontal bars indicate the redshift range for each sample. Black lines: the NFW concentration in the sample of relaxed haloes from Duffy et al. (2008) as a function of redshift. Dotted and dashed: haloes of a given mass as a function of redshift. Solid: NFW concentration of a halo that is evolving in mass, with scatter given by the shaded region.