段小刚. 极坐标视角下的Stein估计量[J]. 应用概率统计, 2025, 41(2): 165-178. DOI: 10.12460/j.issn.1001-4268.aps.2025.2022115
引用本文: 段小刚. 极坐标视角下的Stein估计量[J]. 应用概率统计, 2025, 41(2): 165-178. DOI: 10.12460/j.issn.1001-4268.aps.2025.2022115
DUAN Xiaogang, . Stein Estimator from a Polar Coordinate Perspective[J]. Chinese Journal of Applied Probability and Statistics, 2025, 41(2): 165-178.
Citation: DUAN Xiaogang, . Stein Estimator from a Polar Coordinate Perspective[J]. Chinese Journal of Applied Probability and Statistics, 2025, 41(2): 165-178.

极坐标视角下的Stein估计量

Stein Estimator from a Polar Coordinate Perspective

  • 摘要: 同时估计三个及以上同方差独立正态总体均值时,Stein1证明了最大似然估计平方损失下的不可容许性,并同James显式构造了具有精确一致更优风险函数的压缩型估计量. 这一惊人发现——维数大于等于3时显式结构精确更优压缩型估计量——激发了大量后续研究. Statistical Science期刊2012年组织了一期专刊,“MINIMAX SHRINKAGE ESTIMATION: A TRIBUTE TO CHARLES STEIN”,表达对Stein发现的持续赞美. James和Stein2特定变换和Stein引理3-4是计算Stein估计量风险函数的两种基本途经. 本文基于极坐标变换,对Stein估计量临界维数给出了解释,并提供了其风险函数计算的备用方式. 极坐标变换既可以作为已有方法的补充,其本身在使用Stein引理验证绝对可积性时也发挥着重要作用. 对异方差正态模型均值参数的同时估计,文献上相对缺乏兼具显式结构和精确更优风险函数的相关研究. 本文在Stein原始估计量构成基础上,提出了一类显式估计量,并通过计算和观察其风险函数讨论了各待定系数的选取问题. 本文为进一步认识Stein发现提供了有益补充.

     

    Abstract: For simultaneously estimating three or more mean parameters from independent normal distributions with a common variance, Stein1 proved the inadmissibility of the usual estimator, and constructed jointly with James a uniformly better estimator in the sense of mean squared error loss with a closed-form expression. This astonishing discovery—better uniformly with explicit form when parameter dimension ≥ 3 has inspired a large amount of ongoing research. Statistical Science organized a special issue in 2012, "MINIMAX SHRINKAGE ESTIMATION: A TRIBUTE TO CHARLES STEIN", to express continuing tribute to Charles Stein. The carefully designed transformation of James and Stein2 and Stein's basic lemma3-4 are two basic approaches to computing the risk function of Stein's rule. This paper provides a third approach for solving this problem from a polar coordinate perspective. The new perspective is a useful complement in its own right, and meanwhile plays an important role for checking absolute integrability in the course of using Stein's lemma. Besides, there is relatively little work in the literature focusing specifically on heteroscedastic normal models that are as elegant as Stein's original work, with closed-form expressions and exact risk computations. To this end, we provide a class of estimators with explicit structure inspired by James and Stein's original construct, and find the most appropriate values of coeffcients among this class by direct computing and matching. The findings in this paper provide a useful reference for further studies in this direction.

     

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