The Mann-Whitney U test is a nonparametric alternative to the t test used when a researcher wishes to analyze ranked data. The researcher intermingles the scores of the two groups and then ranks them as if they were all from just one group. The test produces a value (U), whose probability of occurrence is then checked by the researcher in the appropriate statistical table. The logic of the test is as follows: If the two groups are essentially similar, then the sum of the pooled rankings for each group should be about the same. If the summed ranks are markedly different, on the other hand, then this difference is likely to be statistically significant.