The exact null distribution of the Wilcoxon test statistic (obtained via permutations; gray) on two pairs from the Frangieh IFN- gamma data. The Wilcoxon test (and thus Seurat-Wilcox) approximates the exact null distribution using a standard Gaussian density (purple). For pair 1 (left), the Gaussian approximation to the exact null distribution is good (goodness of fit KS statistic = 0.008), while for pair 2 (right) the approximation is inadequate (goodness of fit KS statistic = 0.193).
