ABSTRACT
In looking at differences between two variables, the variable which we use to form our comparison groups usually has a small number of values or levels, say between two and six. We shall call this the comparison-group variable to distinguish it from the other one, which we shall refer to as the criterion variable. The comparison variable is sometimes known as the independent variable, and the criterion variable as the dependent one. An example of a comparison group variable would be gender if we wanted to compare men with women. This typically has two levels (i.e. men and women) which go to make up two comparison groups. Race or ethnic origin, on the other hand, may take on two or more levels (e.g. Caucasian, Negroid, Asian, and Mongolian), thereby creating two or more comparison groups. Other examples of comparison-group variables include different experimental treatments (for example, drugs versus psychotherapy in treating depression), different points in time (for example, two consecutive months), and the categorisation of participants into various levels on some variable (such as high, intermediate, and low job satisfaction). The other variable is the one that we shall use to make our comparison (for example, income or job satisfaction).
