Runs test is a test for randomness of samples See example 17.1. Z distribution for samples where n1 and n2 are greater than 10. The previously used chi-square test was appropriate for weaker nominal data. Mann-Whitney test is more powerful. Some times called the Wilcoxon-rank sum test.
Null hypothesis is that the two populations have the same mean.
Assumes independent samples and that the distributions are symmetrical. If not symmetric, the median replaces the mean. Data is not matched. Formulate the null hypothesis concerning means or medians. Select samples from each group.