Histograms of key optical-derived properties, shown as: all sources (grey), sources best fit with a power law (black dotted line), sources best fit with a soft excess (red solid line), sources best fit with a warm absorber (blue dot-dash line) and sources best with with partial covering (orange dashed line). Median values for each sub-sample are indicated with vertical lines in corresponding colours. Top left: distributions of bolometric luminosities. Top right: distributions of black hole masses. Bottom left: distributions of FWHM of the Hβ, Mg II, or C IV optical lines. Bottom right: distributions of the Eddington ratios (λ_Edd).