Therefore, when the population distribution is undefined, or violates assumption of parametric tests, non-parametric tests must be used. In attempting to choose a particular significance test, at least three questions should be considered (Emory and Cooper, 1991):
(1) does the test involve one sample, two sample or k samples?
(2) If two samples or k samples are involved, are the individual cases
independent or related?
(3) Is the measurement scale nominal, ordinal, interval or ratio?