a numerical index reflecting the degree of linear relationship between two variables. It is scaled so that the value of +1 indicates a perfect positive relationship (such that high scores on variable x are associated with high scores on variable y), –1 indicates a perfect negative relationship (such that high scores on variable x are associated with low scores on variable y, or vice versa), and 0 indicates no relationship. The most commonly used type of correlation coefficient is the Pearson product-moment correlation coefficient.