Correlation

A correlation represents the sign (i.e., direction) and magnitude (i.e., strength) of an association between two variables. There are different types of correlations we can estimate, and their appropriateness will depend on the measurement scales of the two variables. For instance, the Pearson product-moment correlation is used when both variables are continuous (i.e., have interval or ratio measurement scale), whereas the biserial correlation is used when one variable is continuous and the other is dichotomous (e.g., has a nominal measurement scale with just two levels or categories).
For more information on correlations, check out: rforhr.com/cri...
For more information on measurement scales, check out: rforhr.com/des...