Measuring Correlation in Ordered Two-Way Contingency Tables

Abstract

The product moment correlation coefficient is often used even for ordinal data with only a few scale steps. This procedure may lead to biased results, where the bias depends on the number of scale steps and on the skewnesses of the observed variables. The polychoric correlation coefficient, which is a generalization of the tetrachoric correlation to the general case, is discussed as a possible measure of correlation for this kind of data.