General saddlepoint approximations to distributions under an elliptical population

General saddlepoint approximations are derived for the distributions of statistics under an elliptical population. The technique is applied to obtain the tail probabilities of latent roots of a sample covariance matrix. It is shown that the method based on normalizing transformations by Tsuchiya and Konishi (1997) is efficient for the sample correlation coefficient in an elliptical sample.     

A suggestion for measuring heteroskedasticity

The lack of a generally-accepted measure of the degree of severity of heteroskedasticity is shown to have caused some Monte Carlo studies to draw misleading conclusions. An attractive measure of heteroskedasticity is suggested.     

Modified product estimators of finite population mean in finite sampling

With respect to random sampling from finite population, when the correlation between the auxiliary and the main characteristics is negative, the product estimator is often used to estimate the population mean. The product estimator, however, would have a large mean-squared-error (MSE) if the coefficients of variations for these two characteristics were large and the absolute value of the correlation between them was small. In this paper, we propose a general family of modified product estimators, that include the product estimator as a special case. We provide a discussion on the reduction of the MSE by using the optimal modified product estimator that has the minimal MSE in the proposed family. In certain situations, these reductions of the MSE can be significant.     

Regression Coefficient Estimation in Dual Frame Surveys

Dual frame surveys, in which independent samples are selected from two frames to decrease survey costs or to improve coverage, can present challenges for regression coefficient estimation because of complex designs and unknown degree of overlap. In this research, we developed four regression coefficient estimators in dual frame surveys. Simulation results show that all the proposed methods work well.     

基于面板数据的陕西省农村居民消费结构分析

采用个体固定效应变系数模型研究陕西省农村居民消费结构。使用2005--2009年数据，对陕西省农村居民人均消费值进行实证分析。结果表明：在自发人均消费支出中，住房支出位居首位，其次是食品、医疗保健、文教娱乐项目；在人均可支配收入系数之中，低收入者的食品、居住、家庭设备系数值相对中、高收入者要大。比较而言，高收入者在衣着、医疗保健、文化娱乐上的系数值要高；在受上年度人均消费支出影响方面，食品、交通通讯支出影响不显著。     

Statistical Properties of Generalized Gini Coefficient with Application to Health Inequality Measurement

In this article, we report statistical properties of two classes of generalized Gini coefficients (G1 and G2). The theoretical results were assessed via Monte Carlo simulations. Further, we used G1 and G2 on life expectancy to measure health inequalities among the provinces of China and the states of the United States. For China, the results indicated that there was statistically significant health inequality by both G1 and G2. However, for the US, the results showed that there was significant health inequality by G1 but no statistical significance was found in health inequality by G2. Overall, from our study, China has higher health inequality than the United States.     

Two new confidence intervals for the coefficient of variation in a normal distribution

In this article we introduce an approximately unbiased estimator for the population coefficient of variation, τ, in a normal distribution. The accuracy of this estimator is examined by several criteria. Using this estimator and its variance, two approximate confidence intervals for τ are introduced. The performance of the new confidence intervals is compared to those obtained by current methods.     

Coefficients of determinations for variable selection in the msae regression

Our objective is to modify a robust coefficient of determination for the minimum sum of absolute errors MSAE regression proposed by McKean and Sievers (1987) so that it satisfies all the desirable properties. We also propose an adjusted coefficient of determination that is appropriate for comparing several models with different number of variables. Further, it has the property that if it decreases with the addition of predictor variables to the model, then the contribution of these variables is statistically non-significant. We illustrate the results with an example.     

Annual Midwest Conference in Chicago

Simple teaching aids are used to help students understand and appreciate what a transformation is and what a Jacobian is. The teaching aids are effective and easy to make.     

同时按K和〔γ〕设计曲柄摇杆机构的解析法

阐述了一种同时按行程速度变化系数K和许用传动角〔γ〕设计曲柄摇杆机构的解析法 .该方法简单、明了 ,能根据机构的传动质量要求预先确定许用传动角〔γ〕 ,又可避免因出现γmin 的位置与机构两极限位置不重合而引起的计算繁杂问题 .