ABSTRACT
This chapter explains the coefficient of determination, which measures the percentage of the variance in one variable accounted for by the variance in the other variable. It shows that computationally the coefficient of determine is r squared. While Cohen's d is used to measure the effect size for means comparisons, the coefficient of determination is useful when interpreting a Pearson r in understanding how much of the unknown in one variable is explained by another variable or variables. The coefficient of determination, when converted to a percentage, indicates how much variance on one variable is accounted for by the variance on the other. Thus, the coefficient of determination, when converted to a percentage, tells students how effective one variable is in predicting another expressed in terms of percentages.
