Correlation is a statistical measure of the relationship, or association, between two or more variables. There are many different types of correlations, each of which measures particular statistical relationships among and between quantitative variables. Examples of different types of correlations include Pearson's correlation (sometimes called "product-moment correlation"), Spearman's correlation, Kendall's correlation, intra-class correlation, point-biserial correlation and others. The nature of the data (e.g. continuous versus dichoto-mous), the kind of information desired, and other factors can help determine the type of correlation measure that is most appropriate for a particular analysis.

The value of the correlation between any two variables is typically given by a correlation coefficient, which can take on any value between and including − 1.00 (indicating a perfect negative relationship) up to and ...