More on the Preliminary Test Estimator in Almost Unbiased Liu Regression

This article is concerned with the parameter estimation in linear regression model when it is suspected that the regression coefficients are the subspace of the equality restrictions. The objective of this article is to introduce the preliminary test almost unbiased Liu estimators (PTAULE) based on the Wald (W), the likelihood ratio (LR), and the Lagrangian multiplier (LM) tests and compare the proposed estimators in the sense of the quadratic bias and mean square error (MSE) criterion.     

PMSE performance of two different types of preliminary test estimators under a multivariate t error term

Abstract

In this paper, assuming that the error terms follow a multivariate t distribution, we derive the exact formula for the predictive mean squared error (PMSE) of two different types of pretest estimators. It is shown analytically that one of the pretest estimator dominates the SR estimator if a critical value of the pretest is chosen appropriately. Also, we compare the PMSE of the pretest estimators with the MMSE, AMMSE, SR and PSR estimators by numerical evaluations. Our results show that the pretest estimators dominate the OLS estimator for all combinations when the degrees of freedom is not more than 5.     

U-Statistics and Their Asymptotic Results for Some Inequality and Poverty Measures

U-statistics form a general class of statistics that have certain important features in common. This class arises as a generalization of the sample mean and the sample variance, and typically members of the class are asymptotically normal with good consistency properties. The class encompasses some widely used income inequality and poverty measures, in particular the variance, the Gini index, the poverty rate, the average poverty gap ratios, the Foster-Greer-Thorbecke index, and the Sen index and its modified form. This paper illustrates how these measures come together within the class of U-statistics, and thereby why U-statistics are useful in econometrics.     

Estimation of Main Effect When Covariates Have Non-Proportional Hazards

The Cox proportional hazards (PH) regression model has been widely used to analyze survival data in clinical trials and observational studies. In addition to estimating the main treatment or exposure group effect, it is common to adjust for additional covariates using the Cox model. It is well known that violation of the PH assumption can lead to estimates that are biased and difficult to interpret, and model checking has become a routine procedure. However, such checking might focus on the primary group comparisons, and the assumption can still be violated when adjusting for many of the potential covariates. We study the effect of violation of the PH assumption of the covariates on the estimation of the main group effect in the Cox model. The results are summarized in terms of the bias and the coverage properties of the confidence intervals. Overall in randomized clinical trials, the bias caused by misspecifying the PH assumption on the covariates is no more than 15% in absolute value regardless of sample size. In observational studies where the covariates are likely correlated with the group variable, however, the bias can be very severe. The coverage properties largely depend on sample size, as expected, as bias becomes dominating with increasing sample size. These findings should serve as cautionary notes when adjusting for potential confounders in observational studies, as the violation of PH assumption on the confounders can lead to erroneous results.     

数字经济对我国市域农业经济韧性的影响效应与机理分析——基于系统GMM模型与动态门槛模型的检验

基于2011—2019年我国277个市域农业的面板数据,运用反事实方法科学测度了其经济韧性水平,并借助系统GMM模型、中介模型和动态门槛模型等方法,实证检验了数字经济对市域农业经济韧性的影响效应及作用机理。研究发现：数字经济显著增强了市域农业经济韧性,这一结论经一系列稳健性检验后仍能成立;机制分析结果表明,农业资本深化是数字经济提升市域农业经济韧性的重要路径。异质性分析表明,在东部、中部、西部地区和人力资本水平较高的地区,数字经济对市域农业经济韧性的影响效应更为显著,而对东北部地区的提升效应则不显著。动态门槛检验进一步揭示,数字经济对市域农业经济韧性的影响呈现边际递增的非线性特征,当数字经济发展水平越过特定门槛值（0147）时,数字经济对市域农业经济韧性的促进作用显著增强。     

京津冀城市圈公共服务供给水平测度及其区域差异分析

京津冀公共服务一体化是突破京津冀发展瓶颈,推动京津冀区域协同发展的重要抓手之一。本文以京津冀城市圈13个城市为研究区域,通过构建公共服务供给水平的评价指标体系,利用熵值法测度了2014-2017年京津冀城市圈各城市的公共服务供给水平,并对其呈现出的区域格局及区域差异进行探讨,结果显示:京津冀城市圈不同城市间公共服务供给水平差异显著,呈现出以北京和天津为中心逐渐衰减的空间格局;2014-2017年京津冀城市圈不同城市间公共服务供给水平的区域差异逐渐缩小,公共服务供给水平由不均衡格局逐渐向均衡格局演进。本文研究结果为推进京津冀城市圈公共服务协调发展提供建议参考。     

提高矮个篮球中锋的进攻能力

自从篮球运动在世界上广泛开展以来,中锋的位置,一直被高大队员所占据。作者针对某些球队因中锋身材不够高而影响内线攻击力等情况,提出自己的观点,特别指出,在训练中,中锋在思想作风、技术、战术及心理方面所要着重解决的问题和方法,     

汽轮发电机转子静挠度的多元统计分析

讨论了如何用多元线性回归分析的统计方法与有限元法相结合,计算发电机组转子的热应变、基础负载沉降及支承预诸因素影响下的静挠曲线。     

国有商业银行贷款风险现状分析及优化策略

运用现代商业银行管理理论,对国有商业银行贷款风险的现状与成因进行了分析与探索,并就国有商业银行贷款风险的控制及优化策略作了论述,