Standard errors for EM estimation

The EM algorithm is a popular method for computing maximum likelihood estimates. One of its drawbacks is that it does not produce standard errors as a by-product. We consider obtaining standard errors by numerical differentiation. Two approaches are considered. The first differentiates the Fisher score vector to yield the Hessian of the log-likelihood. The second differentiates the EM operator and uses an identity that relates its derivative to the Hessian of the log-likelihood. The well-known SEM algorithm uses the second approach. We consider three additional algorithms: one that uses the first approach and two that use the second. We evaluate the complexity and precision of these three and the SEM in algorithm seven examples. The first is a single-parameter example used to give insight. The others are three examples in each of two areas of EM application: Poisson mixture models and the estimation of covariance from incomplete data. The examples show that there are algorithms that are much simpler and more accurate than the SEM algorithm. Hopefully their simplicity will increase the availability of standard error estimates in EM applications. It is shown that, as previously conjectured, a symmetry diagnostic can accurately estimate errors arising from numerical differentiation. Some issues related to the speed of the EM algorithm and algorithms that differentiate the EM operator are identified.     

A multivariate zero-inflated binomial model for the analysis of correlated proportional data

In this paper, a new multivariate zero-inflated binomial (MZIB) distribution is proposed to analyse the correlated proportional data with excessive zeros. The distributional properties of purposed model are studied. The Fisher scoring algorithm and EM algorithm are given for the computation of estimates of parameters in the proposed MZIB model with/without covariates. The score tests and the likelihood ratio tests are derived for assessing both the zero-inflation and the equality of multiple binomial probabilities in correlated proportional data. A limited simulation study is performed to evaluate the performance of derived EM algorithms for the estimation of parameters in the model with/without covariates and to compare the nominal levels and powers of both score tests and likelihood ratio tests. The whitefly data is used to illustrate the proposed methodologies.     

心理词汇结构表征与二语产出性词汇能力发展

母语心理词汇结构表征与二语心理词汇结构表征存在差异。母语心理词汇中词与词是以语义为联系的,而二语心理词汇中词与词的联系是语音起主要作用。学习者的二语产出性词汇能力到了某一阶段后出现"停滞现象",因此,为促进二语产出性词汇能力的发展,二语学习者有必要重组二语心理词汇结构并加深对单词的语义理解,不断地积累该词与其他词的语义联系。     

中国行政效率的公共选择理论分析

从公共选择理论看来,政府在弥补市场失灵的同时,自身也会产生失灵。但是,中国在从计划经济向市场经济转型过程中,政府行政低效问题主要原因在于自身制度不够完善,如组织的约束机制和组织监控机制的不完善等。主要表现为政府决策达不到帕累托最优、无法评价市场机制与政府干预,何者的作用更大等。因此,必须通过引入竞争机制、进行成本-受益分析和加强监督等措施加以解决。     

＂贫困＂的多模态表征

本文以中介话语分析、多模态社会符号学为理论框架从语言、图像两方面探讨"贫困"现象的话语表征方式。基于BNC语料库揭示"贫困"的词汇语法模式,在语篇层面以媒体对贫困弱势群体表征为例分析其语篇语法,并探讨新闻报道中与"贫困"相关的视觉语法。"贫困"不仅仅表征为穷者匮乏的物质存在,更表征所映现的符号状态和人类精神。     

关于三分Cantor集的结构的一些新结论

旨在采用代数的方法来研究三分Cantor集的结构特点。主要结果除了给出三分Cantor集的代数构造外还定义了仿四进位；结合代数构造、拓扑构造以及仿四进位分别给出并证明了三分Cantor集及其余集的结构公式，从而改进了已有的结论。     

写作表述的三级范式

写作表述在文句、层次和篇章等三个层级上都有一定的范式。表述范式在不同基本文体的层次范式之间、篇章范式之间,以及篇章范式和层次范式之间,虽然各有不同,但也有共同之处。这些表述范式分别都是其同类相仿的写作表述模式构造,能为写作者实施写作表述提供可以借鉴的基本经验。     

从"Representation"看人类学"表述危机"

本文通过对于人类学中的一个重要概念“representation”的梳理,探讨了其在人类学不同阶段理论背景下的不同内涵以及在人类学本体论、认识论、方法论方面的意义,透过“representation”反映出人类学理论从现代主义到后现代主义的发展过程中,尤其是后现代主义思潮下人类学“表述危机”的理论论争的根源和问题的实质。     

纳西族空间观念之色彩表象

空间是抽象的 ,只有对它们进行具体的表象 ,才能将抽象还原成具体。无论在纳西族民俗中 ,还是在其他民族的民俗中 ,色彩常常成为对空间方位进行表象的具体手段之一。由色彩所表象的空间不仅决定着民俗活动的性质 ,也规范着民俗活动的形式与内容。本文从前空间、原空间等方面对纳西族民俗中空间的色彩表象作了介绍和分析