Ratios of ETG number densities at a given redshift with respect to the z ~ 0 true luminosity function in the numerical simulation. The horizontal solid line shows the unit ratio. The solid squares show the results from the mocks for the r-band from PML estimates of the LF; the errorbars are shown only for this case for clarity (and were scaled to an area of 0.25 sq. degrees). The crosses show the results from the photo-z maximum likelihood measurement. The open symbols show the results from the 1/V_max weighted estimates of the mock LFs, obtained using the true redshifts (open squares), the photometric redshifts (open circles), and the photo-zs convolved with their uncertainties (open triangles). Small displacements along the x-axis were added for clarity. The dashed lines correspond to the evolution inferred from the De Lucia et al. (2006) semi-analytic model (coincident with the evolution enforced in our model galaxies; see the text). The grey shaded area shows the estimated cosmic variance in a 0.25 sq. degree light-cone survey divided into slices of Δz = 0.1. Top panel: samples of bright ETG galaxies. Lower panels: faint ETGs; the dotted vertical line shows the redshift limit for accurate faint ratios.