APA Dictionary of Psychology

(symbol: ρ; r_s) a nonparametric measure of statistical dependence between two variables that were measured on an ordinal scale; that is, the individual observations (cases) can be ranked into two ordered series. The Spearman correlation coefficient assesses how well the relationship between the variables can be described using a monotonic function. It ranges in value from +1 to −1. Also called Spearman’s rank correlation coefficient; Spearman’s rho. [Charles Spearman]