Abstract #302103

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JSM 2003 Abstract #302103
Activity Number: 29
Type: Contributed
Date/Time: Sunday, August 3, 2003 : 2:00 PM to 3:50 PM
Sponsor: Biometrics Section
Abstract - #302103
Title: Investigation of Tests for the Difference of Two Spreads
Author(s): Darryl V. Creel*+ and James E. Gentle and Clifton D. Sutton
Companies: Mathematica Policy Research, Inc. and George Mason University and George Mason University
Address: 4877 Chevy Chase Dr., Chevy Chase, MD, 20815,
Keywords: spread ; F test ; robustness
Abstract:

The difference of two spreads is of interest in its own right as well as an assumption in applied statistics. The difference of two population spreads can be estimated from samples of the two populations. The most common test of this type is the F test. The F test has the assumption that the two populations are normally distributed and is extremely sensitive to departures from this assumption. Because of this limitation of the F test, other tests based on normal theory, e.g., Bartlett's test, Hartley's test, and Cochran's test have been developed. Along with the tests based on normal theory, numerous robust tests have been developed, e.g., Levene's test and the Box-Anderson test. General techniques such as jackknife and bootstrap have also been applied to this problem. The aforementioned tests and techniques, including two other tested based on the ratio of median absolute deviations and the ratio of fourth spreads, will be investigated using Monte Carlo simulation. The simulation will involve systematic deviations from the normal distribution, different groups of sample sizes, and different ratios of the spread. We will investigate the validity and power of the tests.

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