Spearman rankorder correlation is a nonparametric measure of association based on the ranks of the data values. The formula is

where is the rank of , is the rank of , is the mean of the values, and is the mean of the values.
PROC CORR computes the Spearman correlation by ranking the data and using the ranks in the Pearson productmoment correlation formula. In case of ties, the averaged ranks are used.