Nonparametric discriminant analysis for the mean unsigned magnetic flux, , for a subset of regions with matched distributions of magnetic flux, in the same format as Figure 1. By construction of the subset, the distributions of PE and NE regions are closely matched, as seen in the left panel. Thus the Peirce skill score is consistent with 0 for time intervals 0–3, as it should be for matched distributions, with a slight increase at the final time interval likely due to the onset of emergence during time interval 4 for some regions.