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Table 4 Mean rejection rates (%) of the t- and WMW tests, averaged over 32 combinations of amount of skewness and standard deviation ratios

From: t-tests, non-parametric tests, and large studies—a paradox of statistical practice?

  Number of subjects in each group
  10 25 50 100 250 500 1000
 Gamma distributions
t-test 4.01 4.71 4.91 4.98 4.95 4.99 4.97
WMW test 9.47 18.0 28.9 41.6 56.9 66.3 74.7
 Lognormal distributions
t-test 4.20 4.69 4.83 4.89 4.95 4.92 4.98
WMW test 5.21 6.99 9.63 14.4 26.5 39.7 54.3