Practical Data Analysis with JMP®

Using JMP to Compare Two Variances

In our earlier discussion of the t-test we noted that there are two versions of the test, corresponding to the conditions in which the samples share the same variance or have different variances. Both in the t-tests and in techniques we'll see later, we may need to decide whether two or more groups have equal or unequal variances before we choose a statistical procedure. The Fit Y by X platform in JMP includes a command that facilitates the judgment.

Let's shift back to the NHANES data, and consider the Body Mass Index (BMI) for the adult men and women in the samples. BMI is a measure of body fat as a percentage of total weight. A lean person has lower BMI than an overweight person. We'll test the hypothesis ...