Sum,product and ratio of Pareto and gamma variables

The exact distributions of X+Y, X Y and X/(X+Y) are studied when X and Y are independent Pareto and gamma random variables. Applications are discussed, to real problems in clinical trials, computer networks and economics.     

A comparative study of confidence intervals for negative binomial proportion

In this paper, we investigate four existing and three new confidence interval estimators for the negative binomial proportion (i.e., proportion under inverse/negative binomial sampling). An extensive and systematic comparative study among these confidence interval estimators through Monte Carlo simulations is presented. The performance of these confidence intervals are evaluated in terms of their coverage probabilities and expected interval widths. Our simulation studies suggest that the confidence interval estimator based on saddlepoint approximation is more appealing for large coverage levels (e.g., nominal level≤1% ) whereas the score confidence interval estimator is more desirable for those commonly used coverage levels (e.g., nominal level>1% ). We illustrate these confidence interval construction methods with a real data set from a maternal congenital heart disease study.     

Testing variance components in balanced linear growth curve models

It is well known that the testing of zero variance components is a non-standard problem since the null hypothesis is on the boundary of the parameter space. The usual asymptotic chi-square distribution of the likelihood ratio and score statistics under the null does not necessarily hold because of this null hypothesis. To circumvent this difficulty in balanced linear growth curve models, we introduce an appropriate test statistic and suggest a permutation procedure to approximate its finite-sample distribution. The proposed test alleviates the necessity of any distributional assumptions for the random effects and errors and can easily be applied for testing multiple variance components. Our simulation studies show that the proposed test has Type I error rate close to the nominal level. The power of the proposed test is also compared with the likelihood ratio test in the simulations. An application on data from an orthodontic study is presented and discussed.     

Two non parametric methods for change-point detection in distribution

The change-point detection problem is determining whether a change has taken place. Two non parametric methods based on empirical likelihood and the likelihood ratio are proposed for detecting a change-point problem in distributions for independent observations. Numerical studies are carried out to evaluate the performance of the proposed methods. The simulation results demonstrate that the proposed methods are robust, that is, they perform well regardless of whether the observations are from the same distribution family.     

欧洲债务危机的主要成因分析

肇始于希腊的欧洲债务危机到目前为止都没有停息的迹象,甚至还呈蔓延之势。欧洲债务危机爆发的直接原因是在金融危机的背景下,政府支出规模持续扩大,导致财政赤字居高不下,最终使得国债规模超过政府的偿还能力,出现明显的违约可能性。同时,国际竞争力不足,导致出口受阻,使得资金问题更加严重。从更深层次看,产业结构不合理,经济发展速度缓慢,过低的投资率和储蓄率及过高的储蓄投资转化率,都是导致欧债危机的重要原因。     

天然岩芯化学驱采收率机理的一些认识

用牛顿流体驱替一定的均质多孔介质系统结果显示，驱油效率由驱替液的毛管数决定。用化学液驱替天然岩芯时，除毛管数以外，还有很多其他因素影响驱油效率。天然岩芯，即使在宏观上是均匀的，在微观上也不均匀；驱替时所得到的效率一般被称为驱油效率，实质上是微观波及效率和驱油效率的乘积。牛顿流体没有弹性，驱替时，体系的润湿性不发生变化，不出现渗吸作用，不形成乳液，孔隙的几何形状不发生变化。但是，用化学液驱替天然岩芯时，由于化学液为粘弹性，体系有润湿性的改变，会出现乳化现象，渗吸作用也会出现。上述因素都会影响驱油效率，尤其是当多种因素同时作用时。分析了极限采收率和经济采收率的区别。很多文章都论述极限采收率，但经济采收率对油田的作用更大。化学驱应考虑上述因素，这对设计、开发、筛选化学剂以及确定驱油体系会是有益的，将深化我们对化学驱机理的认识，促进这方面更深入的研究。     

The estimation of treatment effect for the censored bivariate data under the univariate censoring

This paper establishes a nonparametric estimator for the treatment effect on censored bivariate data under unvariate censoring. This proposed estimator is based on the one from Lin and Ying(1993)'s nonparametric bivariate survival function estimator, which is itself a generalized version of Park and Park(1995)' quantile estimator. A Bahadur type representation of quantile functions were obtained from the marginal survival distribution estimator of Lin and Ying' model. The asymptotic property of this estimator is shown below and the simulation studies are also given     

Changepoint Estimation in a Segmented Linear Regression via Empirical Likelihood

For a segmented regression system with an unknown changepoint over two domains of a predictor, a new empirical likelihood ratio statistic is proposed to test the null hypothesis of no change. Under the null hypothesis of no change, the proposed test statistic is shown empirically to be Gumbel distributed with robust location and scale estimators against various parameter settings and error distributions. A power analysis is conducted to illustrate the performance of the test. Under the alternative hypothesis with a changepoint, the test statistic is utilized to estimate the changepoint between the two domains. A comparison of the frequency distributions between the proposed estimator and two parametric methods indicates that the proposed method is effective in capturing the true changepoint.     

试论金代的桑税

金代桑税渊源于辽和北宋的桑税制度.金代在继承辽宋桑税制度的同时,也进一步发展了自己的桑税制度.这表现为:一方面金代两税中的全部税绢都依据桑税征收,从而提高了它在两税中的地位;另一方面金代确立了旨在规定民户最低桑税额的桑地制度.金代桑税并非"户调",而是金代土地税的基本内容,也是金代两税的重要组成部分.     

英国扩大留学生规模背景下的质量问题及反思

20世纪80年代以来,英国政府将扩大留学生规模作为高等教育国际化发展的重要战略政策。通过对近20年来英国留学生人数、留学生入学标准、优质学位授予比例、生师比、教育生均经费等数据变化趋势的分析,提出在这一经济利益驱动留学生规模扩张的过程中,英国留学生质量要求和标准正在放宽。如何使学生增长速度与优质资源生长速度相匹配、如何在获取短期经济效益的同时寻求高等教育长期可持续性发展的途径,是需要思考和解决的问题。