APA Dictionary of Psychology

(symbol: r²) a numerical index that reflects the proportion of variation in an outcome or response variable that is accounted for by its relationship with a predictor variable. More specifically, it is a measure of the percentage of variance in a dependent variable that is accounted for by its linear relationship with a single independent variable. Obtained by multiplying the value of the correlation coefficient (r) by itself, the coefficient of determination ranges in value from 0 to 1. Low values indicate the outcome is relatively unrelated to the predictor, whereas values closer to 1 indicate that the two variables are highly related. For example, if r = .30, then the squared correlation coefficient is .30² = .09 and interpreted to mean 9% of the variance between the two variables is common or overlapping. Also called determination coefficient; squared correlation coefficient.