Computes Dunn's test (1964) for stochastic superiority and reports the results among multiple pairwise comparisons after a Kruskal-Wallis test for stochastic superiority among k groups (Kruskal and Wallis, 1952). 'dunn.test' makes k(k-1)/2 multiple pairwise comparisons based on Dunn's z-test-statistic approximations to the actual rank statistics. The null hypothesis for each pairwise comparison is that the probability of observing a randomly selected value from the first group that is larger than a randomly selected value from the second group equals one half; this null hypothesis corresponds to that of the Wilcoxon-Mann-Whitney rank-sum test. 'dunn.test' accounts for tied ranks.