ABSTRACT
This chapter is concerned with simple graphical methods for understanding the association between two categorical variables. Most methods of statistical analysis are concerned with understanding relationships or dependence among variables. With categorical variables, these relationships are often studied from data that has been summarized by a contingency table in table form or frequency form, giving the frequencies of observations cross-classified by two or more such variables. The trilinear plot is a specialized display for a 3-column contingency table or for three variables whose relative proportions are to be displayed. The table below contains a weak, non-significant general association, but significant row mean differences and linear associations. The fourfold display is a special case of a radial diagram designed for the display of 2×2 tables. The observer agreement chart proposed by Bangdiwala provides a simple graphic representation of the strength of agreement in a contingency table, and alternative measures of strength of agreement with an intuitive interpretation.
