Today's use of the term, regression, has nothing to do with the biological phenomena observed by Galton. Instead, regression refers to the prediction of one measurement based on knowledge of another. The regression techniques used now were pioneered by Karl Pearson. The most commonly used correlation technique used today is called the Pearson product-moment correlation coefficient. It is applied to data which is at the level of numerical discrete or continuous.
Categorical data requires other correlation techniques such as the contingency coefficient.
Full ranking scale data may be analyzed using the rank-order correlation methods. Before addressing the computational methods, consider the conceptual basis of correlation. Imagine a group comprised of N members. Subject2 X2 Y2 Subject3 X3 Y3 . Again, consider the scores ranked in order of their QPE score.