ABSTRACT

In chapter 26, we described statistical methods used to test the significance of a relationship between two variables that were either continuous or had many ordered categories or levels. The purpose of the present chapter is to describe a statistical test, the Pearson chi-square (χ2) test for independence, that examines the relationship between two variables that are dichotomous or nominal level, with a few nonordered categories. Nominal scale data provide less information than interval or ordinal scale data. The finer the gradations on the measurement scale, the more information is transmitted, as long as there is evidence for reliability and validity. We recommend that data not be divided into a few categories if the data are continuous or have a number of ordered levels, unless the measure to be divided has been validated against an external criterion that justifies using “cut points.”