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Testing Hypotheses about Regression Parameters, When the Error Term Is Heteroscedastic

โœ Scribed by Rand R. Wilcox


Publisher
John Wiley and Sons
Year
1999
Tongue
English
Weight
196 KB
Volume
41
Category
Article
ISSN
0323-3847

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โœฆ Synopsis


The paper considers methods for testing H 0 X b 1 F F F b p 0, where b 1 Y F F F Y b p are the slope parameters in a linear regression model with an emphasis on p 2. It is known that even when the usual error term is normal, but heteroscedastic, control over the probability of a type I error can be poor when using the conventional F test in conjunction with the least squares estimator. When the error term is nonnormal, the situation gets worse. Another practical problem is that power can be poor under even slight departures from normality. Liu and Singh (1997) describe a general bootstrap method for making inferences about parameters in a multivariate setting that is based on the general notion of depth. This paper studies the small-sample properties of their method when applied to the problem at hand. It is found that there is a practical advantage to using Tukey's depth versus the Mahalanobis depth when using a particular robust estimator. When using the ordinary least squares estimator, the method improves upon the conventional F test, but practical problems remain when the sample size is less than 60. In simulations, using Tukey's depth with the robust estimator gave the best results, in terms of type I errors, among the five methods studied.


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