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Improving on the James-Stein Positive-Part Estimator

The purpose of this paper is to give an explicit estimator dominating the positive-part James-Stein rule. The James-Stein estimator improves on the "usual" estimator X of a multivariate normal mean vector θ if the dimension p of the problem is at least 3. It has been known since at least 1...

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Bibliographic Details
Published in:The Annals of statistics 1994-09, Vol.22 (3), p.1517-1538
Main Authors: Shao, Peter Yi-Shi, Strawderman, William E.
Format: Article
Language:English
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Summary:The purpose of this paper is to give an explicit estimator dominating the positive-part James-Stein rule. The James-Stein estimator improves on the "usual" estimator X of a multivariate normal mean vector θ if the dimension p of the problem is at least 3. It has been known since at least 1964 that the positive-part version of this estimator improves on the James-Stein estimator. Brown's 1971 results imply that the positive-part version is itself inadmissible although this result was assumed to be true much earlier. Explicit improvements, however, have not previously been found; indeed, 1988 results of Bock and of Brown imply that no estimator dominating the positive-part estimator exists whose unbiased estimator of risk is uniformly smaller than that of the positive-part estimator.
ISSN:0090-5364
2168-8966
DOI:10.1214/aos/1176325640