The Pearson product-moment correlation coefficient is measured on a standard scale -- it can only range between -1.0 and +1.0. As such, we can interpret the correlation coefficient as representing an effect size. It tells us the strength of the relationship between the two variables.

In psychological research, we use Cohen's (1988) conventions to interpret effect size. A correlation coefficient of .10 is thought to represent a weak or small association; a correlation coefficient of .30 is considered a moderate correlation; and a correlation coefficient of .50 or larger is thought to represent a strong or large correlation.