Directions of how to do this in EXCEL:.Intellectus Statistic: see the Nonparametric choice under Analyses.Click here for an example illustration (calculated by hand).Here is some information in the event you want to try to run one (not required for class) The Mann-Whitney U is the nonparametric alternative to the Independent t-test. If the total sample size is seven or less, the Mann-Whitney test will always give a P value greater than 0.05 no matter how much the groups differ. You just have no compelling evidence that they differ. This is not the same as saying that the two populations are the same. If the P value is large, the data do not give you any reason to reject the null hypothesis. If the means of the ranks in the two groups are very different, the P value will be small. It uses the standard normal distributed z-value to test significance- calculating a two sample z statistic, using the pooled variance estimate. Then you average the ranks in each group, and report the two averages. The largest number gets a rank of n, where n is the total number of values in the two groups. To perform the Mann-Whitney test, one first ranks all the values from low to high, paying no attention to which group each value belongs. The Mann-Whitney U (equivalent to Wilcoxon Rank Sum Test/ Wilcoxon 2-sample t-test) test compares the distributions of ranks in two groups. To deal with the non normal data, the values are ranked and similar procedures as in the t-test are used on ranked data. When you have data that are not normally distributed then the assumption of normality is violated and nonparametric tests should be used.
Mann-Whitney U and Wilcoxon Signed-Ranks Tests NRSG 795: BIOSTATISTICS FOR EVIDENCE-BASED PRACTICE Module 5: Significance Testing/Hypothesis Testing for Two Groups
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