Use non-parametric tests when assumptions for parametric tests are not satisfied: normal distribution
homogeneity of variance
ordinal or nominal scale
Two independent sample:
• Mann-Whitney U-test – analogous to parametric t-test – does not require equal sample sizes
Three or more independent samples:
• Kruskall-Wallis one way ANOVA – analogous to one way ANOVA
Two or more correlated sample:
• Sign test
• Wilcoxon signed ranks test
Three or more correlated samples:
• Friedman Two-way analysis of variance by ranks
Cross-tabulated data:
• Fischer’s exact test
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