Number density. Upper panel: number density calculated at 1.4 GHz for a set of different luminosity ranges of the same width, as denoted in the legend above the figure. The black dots represent the maximum value of each line. Middle panel: number density at 1.4 GHz calculated for a set of progressively increasing luminosity ranges, as denoted in the legend above the figure. Lower panel: number density at 1.4 GHz as a function of redshift for a set of different surveys, denoted in the legend. The data points denote the high-redshift quasar surveys as described in the text. The uncertainties in this work are calculated from the resulting samples within the parametric Bayesian method as 90% quantiles. The uncertainties of the literature values were determined as maximum uncertainties of the parameters, as described in the text. The shaded area in the plots denote a higher redshift where the LF models are less constrained. The high-redshift quasar density from Gloudemans et al. (2021) is a lower limit, as the luminosity range of the LF used in the calculation was smaller.