Effective (left) and precession spin (right) probability density functions (pdf) GH (solid blue lines) and no-GH (dashed orange lines) model. We do not apply any selection effects to our simulations. Solid black lines show the posterior distribution inferred from LVK data, after applying a parametric-model description of the intrinsic BBH population with hierarchical Bayesian inference (Abbott et al. 2023b).