Mann-Whitney
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Stat > Nonparametrics > Mann-Whitney

You can perform a 2-sample rank test (also called the Mann-Whitney test, or the two-sample Wilcoxon rank sum test) of the equality of two population medians, and calculate the corresponding point estimate and confidence interval. The hypotheses are

H0: h1 = h2 versus H1: h1 ≠ h2 , where h is the population median.

An assumption for the Mann-Whitney test is that the data are independent random samples from two populations that have the same shape and a scale that is continuous or ordinal (possesses natural ordering) if discrete. The 2-sample rank test is slightly less powerful (the confidence interval is wider on the average) than the 2-sample test with pooled sample variance when the populations are normal, and considerably more powerful (confidence interval is narrower, on the average) for many other populations. If the populations have different shapes or different standard deviations, a 2-Sample t without pooling variances may be more appropriate.

Dialog box items

First Sample: Select the column containing the sample data from one population.

Second Sample: Select the column containing the sample data from the other population.

Confidence level: Specify the level of confidence desired between 0 and 100; the attained level will be as close as possible.

Alternative: Click the arrow to choose the kind of test performed by selecting less than (lower-tailed), not equal (two-tailed), or greater than (upper-tailed) from the drop-down box.