sets : Mann-Whitney U (or Wilcoxon Signed Rank if paired data (replaces paired Student's t-test) Non-normally distributed (non-ordinal, non-nominal), more than two data sets, paired: Friedman 's (don't ask, and don't look. The link is for completeness. You have been warned.) Non-normally distributed (non-ordinal, non-nominal), more than two data sets, unpaired