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Spearman's rank correlation coefficient

Spearman's rank correlation coefficient or ρ (rho) is a non-parametric measure of correlation – that is, it assesses how well a linear equation describes the relationship between two variables without making any assumptions about the frequency distribution of the variables. To calculate , raw scores are converted to ranks. is a special case of the Pearson product-moment correlation coefficient in which the data are ranks, although a simpler formula is often used in calculation by hand:


D = the difference between the ranks of corresponding values of X and Y, and

N = the number of pairs of values.