Normalized histograms showing the distribution of SMBH mass ratio q_• (Equation (12)) calculated from M_•–σ (light blue) and M_•–M_b (dark blue). Panel (a) uses the M_•–M_b and M_•–σ from N. J. McConnell & C.-P. Ma (2013), and panel (b) uses the M_•–M_b and M_•–σ from J. Kormendy & L. C. Ho (2013). The solid black line at q_• = 0.25 divides major and minor SMBH mergers, and the relative fractions of major (f_major) and minor (f_minor) SMBH mergers predicted by each scaling relation are shown as percentages of the total close-pair sample. The Kolmogorov–Smirnov (K-S) statistic (D) between the distributions and the associated p-values are also shown. D is greater in panel (a), indicating a larger statistical difference in the q_• distributions obtained from the N. J. McConnell & C.-P. Ma (2013) scaling relations (likely as a result of the differences in morphology and M_• dynamic range described in Section 2.4). The M_•–M_b scaling relations predict a greater fraction of major SMBH pairs than the M_•–σ scaling relations.