Figure 6: (a) quasar luminosity function, from the work of Glikman et al. . The filled red circles show the measurements presented on that work, while the open red circles were reported previously by the same group  and show the change with increased spectroscopic completeness. The triangles were obtained from the SDSS quasar sample at . The blue squares are the space densities of QSOs from Ikeda et al.  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 , representing different fits to the observed QLF. (b) Quasar space density as a function of redshift, from the work of Ikeda et al. . 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.