Spearman's Rank Correlation
A rank-based correlation coefficient calculated as rs = 1 - (6Σd² / n(n² - 1)), where d is the difference in ranks for each pair and n is the number of pairs.
Real World
A panel of wine judges ranks ten Bordeaux vintages independently; Spearman's rs between two judges' rankings reveals whether their tastes consistently agree, even if their scores aren't on a numeric scale.
Exam Focus
When data are ranks or ordinal, always choose Spearman's over PMCC — state this choice and the reason in your working to gain method marks.
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