

Spearman rank-order 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 product-moment correlation formula. In case of ties, the averaged ranks are used.