Rank order correlation is the study of relationships between different rankings on the same set of items. It deals with measuring correspondence between two rankings, and assessing the statistical significance of this. Two of the main methods were devised by Charles Spearman (1863–1945, a student of Karl Pearson) and Maurice Kendall. Three other tests include the Wilcoxon signed-rank test, Mann-Whitney U test and the Kruskal-Wallis analysis of ranks.
