Scatter plot of the minimum (across events) number of effective samples ﹩\min \left[{N}_{\mathrm{eff},i}\right]﹩ and the width of the zero-spin spike ϵ _spike for the BetaSpike+TruncatedMixture model. Each point represents a single draw from the posterior shown in Figure 6. Left panel: the minimum number of effective samples as computed across the entire population model. Middle panel: the minimum number of effective samples in the “bulk” (Beta distribution) spin magnitude subpopulation.. Right panel: the minimum number of effective samples in the “spike” (zero-spin half-Gaussian) spin magnitude subpopulation. Dashed vertical lines denote ϵ _spike = 0.03, the lower limit we impose on this parameter in our prior. Although the minimum sample count in the spike appears unacceptably low, the minimum is driven by events that are confidently spinning and which therefore do not impact our inference regarding the zero-spin spike (see the left panel of Figure 11). Red points illustrate the minimum effective samples when excluding events these events that are confidently spinning. Green points show the minimum effective sample count if we further exclude events that are “likely” spinning (e.g., middle panel of Figure 11), focusing only on those events that are well described by zero spin. To ensure a reasonable number of effective samples among these remaining events, we bound ϵ _spike > 0.03 and note that the region ϵ _spike ≲ 0.04 may be subject to elevated Monte Carlo variance.