For pain intensity outcomes and effect size of .2, the
average power of theWMWtest (.57) was almost 3 times
larger than for the t-test (.21). For medium effects, the
power of the WMW test (.87) was 34% higher than the
t-test power (.65), and for large effect size, the WMW at power of 1. For a = .01 and .001, the superior power
of the WMW test was even greater as sample sizes
increased.