An analysis of classifier performance based on likely membership of known globular clusters. Sources are selected based on proximity to a known globular cluster from the catalogue of Harris (1996). Distances are computed for all these sources, assuming they are all BHB stars, and compared to the catalogue distance for the cluster. True BHB stars that are really cluster members should return a distance consistent with the cluster distance. Most contaminants from within the cluster will appear too distant compared to the BHB population, because they are fainter. This plot shows the fractional absolute residual in the distance estimate in kpc versus the (prior-corrected) SVM probability P(BHB). The dashed line shows the threshold P(BHB) = 0.5.