Spearman's rank-order coefficient

a statistic measuring the extent to which two sets of discrete data place the distinct items in the same order, given by r S = 1 – 6 Σ d ² /n ( n ² – 1 ), where Σ d ² is the sum of the squares of the differences of ranks between the two orderings and n is the number of items in each Also calledSpearman's rank-order correlation coefficient