The Mann‐Whitney U test is also one of the most
powerful non‐parametric tests (Landers, 1981), where the
statistical power corresponds to the probability of rejecting a
false null hypothesis. This test has thus good probabilities of
providing statistically significant results when the
alternative hypothesis applies to the measured reality. Even
if it is used on average‐size samples (between 10 and 20
observations) or with data that satisfy the constraints of the
t‐test, the Mann‐Whitney has approximately 95% of the
Student’s t‐test statistical power (Landers). By comparison
with the t‐test, the Mann‐Whitney U is less at risk to give a
wrongfully significant result when there is presence of one
or two extreme values in the sample under investigation
(Siegel and Castellan, 1988).