Inferred values of the hyperparameters characterizing the mean (top), standard deviation (middle), and height (bottom) of the Gaussian peak in the black hole mass spectrum as a function of redshift. In each panel, the green traces mark individual hyperposterior samples, and the solid and dot-dashed black curves indicate 95% credible posterior bounds and medians, respectively. The dashed cyan lines analogously illustrate 95% credible prior bounds. Finally, the dotted magenta curves indicate 95% credible prior bounds on each parameter when it is first conditioned on the measured posteriors at z = 0.