Stacked spectra in three equally sized groups (colored lines) divided by α_ox, L_UV, λ_Edd, and M_BH (panels from left to right). The legend gives the mean value of each subgroup. Error bars are obtained with bootstrapping as in Fig. 3, but are generally very small except above ∼8 keV. In the left panel, the three colored lines are indistinguishable above 2 keV. Below 1 keV, the blue data points from the lowest α_ox subsample are always below the pink points from the highest α_ox subsample. The λ_Edd panel shows an even larger spread between subgroups, while it is less pronounced in the L_UV panel and reversed in the M_BH panel.