Correlation Coefficient

The correlation coefficient is used to measure the relationship between two random variables. It provides information about the strength and direction of the correlation varying from -1 to +1, where 0 indicates no relationship, +1 indicates a perfect positive relationship (as one variable increases in value, the other variable also increases in value), and -1 indicates a perfect negative linear relationship (as one variable increases in value, the other variable decreases in value).

The most widely-used type of correlation coefficient is Pearson r (Pearson, 1896), also called linear or product-moment correlation (the term correlation was first used by Galton, 1888). Another measure of a relation between variables is Spearman R, which is computed from ranks.