The Mann-Whitney test is available when the normal assumption underlying the Student t-test is in question. are outliers in the data. The data on weekly run-up (or waste percent) for five suppliers of the Levi-Strauss clothing plant in Albuquerque provides an example. Presence of outliers violates the assum- tions of the the t-test. Students can experiment to see the results of the two tests for pairs of suppliers. Deleting the extreme outliers for Plants 1 and 2 brings the t-test results close to the non-parametric alternative. The same outcome is true for ANOVA compared with the Kruskal-Walls rank-sum test.