Effective spin correlations with relevant BBH parameters. The top row shows the probability density distribution for the primary BH mass, m₁, and the effective spin, χ_eff, compared with posterior contour plots at credibility levels 50% and 90% of LVK BBH merger events GW190521 (dash-dotted red line, Abbott et al. 2020) and GW170729 (solid orange line, Abbott et al. 2023b), and LVK transient event GW190403_051519 (dashed yellow line, Abbott et al. 2021). The central (bottom) row has the same legend as the first row, but shows the mass ratio, q = m₂/m₁, (precession spin, χ_p) and the effective spin, χ_eff.