Usually, the groups in a two-sample t test are fixed by design, and the grouping variable has one value for each group. However, there are times when assignment to one of two groups can be made on the basis of an existing scale variable. For example, consider math and verbal test scores. You would like to perform a t test on verbal scores, using the students above and below a given cutoff score on the math as the independent groups. With the Independent-Samples T Test procedure, all you need to provide is the cut point. The program divides the sample in two at the cut point and performs the t test. The virtue of this method is that the cut point can easily be changed without the need to re-create the grouping variable by hand every time.