Joint Identification of Location and Dispersion Effects in Unreplicated Two-Level Factorials

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Final version will be published in Technometrics ( and will appear in revised form.

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Maximum likelihood
Corrected heteroscedastic information criterion
Model averaging
Exhaustive search

Most procedures that have been proposed to identify dispersion effects in unreplicated factorial designs assume that location effects have been identified correctly. Incorrect identi- fication of location effects may impair subsequent identification of dispersion effects. We develop a model for joint identification of location and dispersion effects that can reliably identify active effects of both types. The joint model is estimated using maximum likelihood, and hence effect selection is done using a specially derived information criterion. An exhaustive search through a limited version of the space of possible models is conducted. Both a single-model output and model averaging are considered. The method is shown to be capable of identifying sensible location-dispersion models that are missed by methods that rely on sequential estimation of location and dispersion effects.

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Natural Sciences and Engineering Research Council of Canada (NSERC)