Figure 6: (a) quasar luminosity function, from the work of Glikman et al. [57]. The filled red circles show the measurements presented on that work, while the open red circles were reported previously by the same group [58] and show the change with increased spectroscopic completeness. The triangles were obtained from the SDSS quasar sample at [56]. The blue squares are the space densities of  QSOs from Ikeda et al. [59] and the dot-dashed line is their best-fit double power law. The lower right-hand legend lists the best-fit parameters to a double power-law (solid line) shaded region represents the uncertainties. Dashed and dotted lines show the QLF [60], representing different fits to the observed QLF. (b) Quasar space density as a function of redshift, from the work of Ikeda et al. [59]. Dotted lines used the combined 2SLAQ, SDSS, SWIRE, NDFWS and DLS samples, while the dashed lines combine the COMOS and 2SLAQ sources. While AGN downsizing is clearly visible at , at higher redshifts the situation is more uncertain.