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AI 根据所提供的论文材料归类:摘要属于线性模型无偏估计量的一般理论,未提供可明确对应所列应用领域细分的证据。

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关注这篇论文的作者
Lihua Lei
Jeffrey Wooldridge

哪些估计量在线性模型中是无偏的?

研究问题
对于不同限制下的线性模型类,哪些估计量能够保持无偏,非线性无偏估计量是否存在,以及相关 Gauss–Markov 扩展为何得出不同结论?
方法与思路
作者回顾早期研究并建立统一记号框架,再针对系数、协方差、矩存在性和误差分布的不同限制,推导无偏估计量的表示定理。
材料陈述的贡献
摘要称,统一框架能够澄清既有研究间的差异,新表示定理推广了相关评论和早期结果,并覆盖多种线性模型限制。
阅读关注点
应核对无偏性要求覆盖的模型类、估计量是否允许非线性、误差分布与矩条件,以及不同版本命题之间的量词和条件差异。
阅读边界
这是 arXiv 预印本,同行评审或期刊接收未获核验;摘要未给出定理形式,关于 Hansen 不同版本的讨论也不能替代原文核验。

原文摘要

The recent thought-provoking paper by Hansen [2022, Econometrica] proved that the Gauss-Markov theorem continues to hold without the requirement that competing estimators are linear in the vector of outcomes. Despite the elegant proof, it was shown by the authors and other researchers that the main result in the earlier version of Hansen's paper does not extend the classic Gauss-Markov theorem because no nonlinear unbiased estimator exists under his conditions. To address the issue, Hansen [2022] added statements in the latest version with new conditions under which nonlinear unbiased estimators exist. Motivated by the lively discussion, we study a fundamental problem: what estimators are unbiased for a given class of linear models? We first review a line of highly relevant work dating back to the 1960s, which, unfortunately, have not drawn enough attention. Then, we introduce notation that allows us to restate and unify results from earlier work and Hansen [2022]. The new framework also allows us to highlight differences among previous conclusions. Lastly, we establish new representation theorems for unbiased estimators under different restrictions on the linear model, allowing the coefficients and covariance matrix to take only a finite number of values, the higher moments of the estimator and the dependent variable to exist, and the error distribution to be discrete, absolutely continuous, or dominated by another probability measure. Our results substantially generalize the claims of parallel commentaries on Hansen [2022] and a remarkable result by Koopmann [1982].

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