Mann-Whitney test
  • The Mann-Whitney test and Wilcoxon rank-sum test compare two conditions when different participants take part in each condition and the resulting data have unusual cases or violate any assumption in Chapter 5.
  • Look at the row labelled Asymptotic Sig. or Exact Sig. (if your sample is small). If the value is less than .05 then the two groups are significantly different.
  • The values of the mean ranks tell you how the groups differ (the group with the highest scores will have the highest mean rank).
  • Report the U statistic (or Ws if you prefer), the corresponding z and the significance value. Also report the medians and their corresponding ranges (or draw a boxplot).
  • Calculate the effect size and report this too.
Wilcoxon signed-rank test
  • The Wilcoxon signed-rank test compares two conditions when the same participants take part in each condition and the resulting data have unusual cases or violate any assumption in Chapter 5.
  • Look at the row labelled Asymptotic Sig.(2-sided test) . If the value is less than .05 then the two conditions are significantly different.
  • Look at the histogram and numbers of positive or negative differences to tell you how the groups differ (the greater number of differences in a particular direction tells you the direction of the result).
  • Report the T-statistic, the corresponding z, the exact significance value and an effect size. Also report the medians and their corresponding ranges (or draw a boxplot).
The Kruskal-Wallis test
  • The Kruskal-Wallis test compares several conditions when different participants take part in each condition and the resulting data have unusual cases or violate any assumption in Chapter 5.
  • Look at the row labelled Asymptotic Sig. If the value is less than .05 then the groups are significantly different.
  • You can follow up the main analysis with pairwise comparisons, comparing each group against each other group in pairs, but correcting the resulting p-value of each test so that the overall error rate remains at 5%.
  • If you predict that the means will increase or decrease across your groups in a certain order then do Jonckheere's trend test.
  • Report the H-statistic, the degrees of freedom and the significance value for the main analysis. For any follow-up tests, report an effect size (you can also report the corresponding z-score and significance value). Also report the medians and their corresponding ranges (or draw a boxplot).
Friedman's ANOVA
  • Friedman's ANOVA compares several conditions when the same participants take part in each condition and the resulting data have unusual cases or violate any assumption in Chapter 5.
  • Look at the row labelled Asymptotic Sig. If the value is less than .05 then the conditions are significantly different.
  • You can follow up the main analysis with pairwise comparisons. Which compare each group against each other group in pairs, but correcting the resulting p-value of each test so that the overall error rate remains at 5%.
  • Report the Χ2 statistic, the degrees of freedom and the significance value for the main analysis. For any follow-up tests, report an effect size (you can also report the corresponding z and the significance value).
  • Report the medians and their ranges (or draw a boxplot).
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