<P> The Spearman correlation between two variables is equal to the Pearson correlation between the rank values of those two variables ; while Pearson 's correlation assesses linear relationships , Spearman 's correlation assesses monotonic relationships ( whether linear or not ) . If there are no repeated data values , a perfect Spearman correlation of + 1 or − 1 occurs when each of the variables is a perfect monotone function of the other . </P>
when is a spearman correlation meant to be used instead of a pearson correlation
assesses monotonic relationships ( whether linear or not )