A note on optimal vector unbiased predictor

A characterization of optimal vector unbiased predictor is obtained. Some properties of optimal unbiased predictors are established. It is shown that simultaneous prediction of future random variables is equivalent to marginal prediction of these random variables. Following Kale and Chandrasekar (1983) and Chandrasekar (1984), it is shown that the criteria proposed by ishii (1969) based on matrices and the one proposed by Bibby and Toutenburg (1977) based on quadratic loss in the class of vector unbiased predictors are equivalent. The above approach is illustrated with some examples.     

A sequential sampling plan for the inverse gaussian mean

The inverse gaussian distribution is a flexible model which has been extensively applied in the theory of generalized linear models and accelerated life testing where early failure times predominate. More recently it has received attention in areas such as quality control, and as an underlying model that provides an alternative to the analysis of variance. In reliability testing and acceptance sampling data acquisition is often in the face of scarce resources and may be both costly and time-consuming. In such settings it is desirable to reach a statistically sound decision as quickly as possible. Based on sequential probability ratio tests (SPRT), sequential sampling plans provide one method of arriving at a timely, statistically based decision. A sequential sampling plan for the inverse gaussian process mean when the value of the shape parameter of the density is known is presented in this paper.     

利用人口普查数据测量社会距离的方法探讨

社会学概念“社会距离”从博格达斯量表开始,其测量的一直是群体（族、阶层）之间的主观心理距离,反映的是群体间文化差异或群体间相互接受程度。为了回应塔尔达和拉梅尔对社会距离概念客观性的要求,本文借鉴重新定义距离这个概念,反映不同社会阶层客观的社会差别,并利用广州市2000年人口普查数据和2005年1％人口抽样调查数据来测量广州市不同阶层（群体）的社会距离,解释广州市社会阶层（群体）关系的变化,说明社会变迁。     

Accounting for dynamic selection bias in educational transitions: The Cameron-Heckman latent class estimator and its generalizations

The sequential logit model of educational transitions has long been the dominant modeling framework for the study of inequality of educational opportunity ever since the seminal works of [Mare, 1980] and [Mare, 1981]. But conventional applications of the model are known to be biased by the ubiquitous presence of unobserved heterogeneity. Cameron and Heckman (1998) propose a logit model that allows for two or three latent classes if the selection bias is solely generated by a person-specific component of stable unobserved heterogeneity. To evaluate the latent class logit regression estimator, this study makes use of simulated data to eliminate the influences of other problems of transition modeling. The simulation is based on five independent pairs of large samples generated from standard distributional assumptions of transition modeling. The new estimator appears to be an effective way to adjust for dynamic selection bias when family background effects are transition-invariant and sample size is in the order of ten thousand or above. By contrast, the conventional sequential logit model produces results that are very different from the data generating models. This study also considers two alternative ways to improve statistical efficiency: (1) incorporate a crude indicator of stable unobserved heterogeneity; (2) pool the effect estimates across transitions, background variables, and alternative estimators to smooth out noise under the null hypothesis of transition invariance. In addition, this study examines the impact of indicator reliability and sample size on the performance of the latent class regression models and suggests practical guidelines.     

Tests for symmetry with right censoring

Permutation tests for symmetry are suggested using data that are subject to right censoring. Such tests are directly relevant to the assumptions that underlie the generalized Wilcoxon test since the symmetric logistic distribution for log-errors has been used to motivate Wilcoxon scores in the censored accelerated failure time model. Its principal competitor is the log-rank (LGR) test motivated by an extreme value error distribution that is positively skewed. The proposed one-sided tests for symmetry against the alternative of positive skewness are directly relevant to the choice between usage of these two tests.

The permutation tests use statistics from the weighted LGR class normally used for making two-sample comparisons. From this class, the test using LGR weights (all weights equal) showed the greatest discriminatory power in simulations that compared the possibility of logistic errors versus extreme value errors.

In the test construction, a median estimate, determined by inverting the Kaplan–Meier estimator, is used to divide the data into a “control” group to its left that is compared with a “treatment” group to its right. As an unavoidable consequence of testing symmetry, data in the control group that have been censored become uninformative in performing this two-sample test. Thus, early heavy censoring of data can reduce the effective sample size of the control group and result in diminished power for discriminating symmetry in the population distribution.     

教师自我效能、集体效能与教师压力状况的关系研究

本研究采用问卷调查法对小学、初中、高中以及职业中学4类学校专职教师的自我效能、集体效能以及工作压力进行了研究,结果表明:1.性别、教龄分段、学校类型等不同的变量水平下教师工作压力水平具有显著的差异。2.教师教学效能感和教师集体效能感存在显著正相关,教师教学效能感和教师集体效能感总分与压力总分之间存在显著负相关。回归分析表明:教师集体效能感总分对工作压力的预测力最强,性别、教龄分段以及教师自我效能感总分也进入回归方程。     

当代中国中产阶层的政治文化发展功能及其实现机制

中产阶层是当代中国政治文化发展重要的实践主体。他们具有支持改革的政治认知倾向、民主与法治的政治文化价值观、积极参与的政治文化态度。他们维系着政治文化发展所需要的稳定的社会环境,体现着当代中国“共同富裕”的价值追求,构筑着全方位的政治合法性资源,推动着政治文化向民主与法治方向发展。他们通过聚合本阶层力量,协调阶层间关系,发挥规范性导向、价值性导向和结构性导向作用,来引领各阶层发展,促进政治文化进步。     

民族院校大学英语课堂教学改革刍议

随着我国大学英语教学改革的不断深化,各校都在探索适合各自特点、符合社会需求的英语教学新路子和新模式。面对新的教材体系,考虑民族院校学生的特点,如何采取有效的方法和措施进行英语课堂教学,探索出一套符合民族学院自身特点的英语课堂教学新模式,已成为每位大学英语教师所面临的课题。     

我国集体林权制度改革中的法制障碍及解决途径

集林权权制度改革是被称之为＂第三次土地改革＂的制度性改革。当前,我国林地所有权和使用权在林改实际操作中没有完全明晰;森林资源资产评估法律制度不健全;与＂托管造林＂相关的法律法规缺失等成为影响集体林权制度改革的法制障碍。破解这些法制障碍,推动我国集体林权制度改革,需要在实践中进一步落实林权的归属,健全完善森林资源资产评估法律制度和与＂托管造林＂相关的法律法规,以促进林地流转规范有序发展。     

唤醒遗忘的记忆——《所罗门之歌》中美国黑人民族主体性建构

虽然经过第一次解放,美国黑人今天依然面临被美国白人主流社会边缘化的危险。文章从主体性视角出发,对托妮·莫里森的名著《所罗门之歌》中黑人的民族主体性建构进行了探讨,指出在彼拉多和吉他的引领下,作为第三代黑人代表的奶人记忆中沉睡的民族性被唤醒,毅然重返黑人世界的精神家园。奶人这一民族主体性重建的成功塑造展现了黑人成长的历史进程。