utest - Mann-Whitney U test
utest [-n] [-t [time]] [-m [samples]] n1 n2 U
utest computes P values for the Mann-Whitney U statistic. The input values are n1 and n2, the size of the two samples, and U, the Mann-Whitney statistic. The output lists two percentages: the probability of obtaining a U greater than or equal to the measured value by chance, followed by the probability of obtaining a U less than or equal to the measured value by chance. The two datasets are significantly different from each other in a one-tailed test at level alpha if the appropriate one of these is less than alpha. (Which one is appropriate will depend on exactly how you calculate U, but it should be obvious from the data whether a difference is in the appropriate direction.) The two datasets are significantly different from each other in a two-tailed test at level alpha if the smaller of the reported Ps is less than alpha/2.
utest has two modes: exact and Monte Carlo. Exact mode is the default. In this mode all possible reassortments of the data are examined to determine exact significance levels. The number of such assortments is N!/(n1! n2!), so exact mode becomes impractically slow as the datasets become large. Monte Carlo mode, specified by the -m option, can be used for large datasets. In this mode reassortments are generated at random.
The -t option is used to set a time limit. If more than the specified time elapses, the calculation is aborted.