A Method to Handle Zero Counts in the Multinomial Model

In the context of an objective Bayesian approach to the multinomial model, Dirichlet(a, …, a) priors with a < 1 have previously been shown to be inadequate in the presence of zero counts, suggesting that the uniform prior (a = 1) is the preferred candidate. In the presence of many zero counts, however, this prior may not be satisfactory either. A model selection approach is proposed, allowing for the possibility of zero parameters corresponding to zero count categories. This approach results in a posterior mixture of Dirichlet distributions and marginal mixtures of beta distributions, which seem to avoid the problems that potentially result from the various proposed Dirichlet priors, in particular in the context of extreme data with zero counts.     

Bayesian Estimation and Model Choice in Item Response Models

Item response models are essential tools for analyzing results from many educational and psychological tests. Such models are used to quantify the probability of correct response as a function of unobserved examinee ability and other parameters explaining the difficulty and the discriminatory power of the questions in the test. Some of these models also incorporate a threshold parameter for the probability of the correct response to account for the effect of guessing the correct answer in multiple choice type tests. In this article we consider fitting of such models using the Gibbs sampler. A data augmentation method to analyze a normal-ogive model incorporating a threshold guessing parameter is introduced and compared with a Metropolis-Hastings sampling method. The proposed method is an order of magnitude more efficient than the existing method. Another objective of this paper is to develop Bayesian model choice techniques for model discrimination. A predictive approach based on a variant of the Bayes factor is used and compared with another decision theoretic method which minimizes an expected loss function on the predictive space. A classical model choice technique based on a modified likelihood ratio test statistic is shown as one component of the second criterion. As a consequence the Bayesian methods proposed in this paper are contrasted with the classical approach based on the likelihood ratio test. Several examples are given to illustrate the methods.     

对我国高校社会工作专业人才培养的思考

2011年11月,中组部等18个部门和组织联合发布《关于加强社会工作专业人才队伍建设的意见》,充分说明国家对社会工作专业人才的高度重视,同时也进一步体现经济社会发展对社会工作专业人才的迫切需求。因此,高质量社会工作专业人才的培养已经成为高等学校的重大课题,本文从人才培养目标定位、服务面向、培养模式构建等三个重要方面切入,提出对我国高校社会工作专业人才培养的思考。     

A Comparative Study of Model-based Tests of Independence for Ordinal Data Using the Bootstrap

When analyzing categorical data using loglinear models in sparse contingency tables, asymptotic results may fail. In this paper the empirical properties of three commonly used asymptotic tests of independence, based on the uniform association model for ordinal data, are investigated by means of Monte Carlo simulation. Five different bootstrapped tests of independence are presented and compared to the asymptotic tests. The comparisons are made with respect to both size and power properties of the tests. Results indicate that the asymptotic tests have poor size control. The test based on the estimated association parameter is severely conservative and the two chi-squared tests (Pearson, likelihood-ratio) are both liberal. The bootstrap tests that either use a parametric assumption or are based on non-pivotal test statistics do not perform better than the asymptotic tests in all situations. The bootstrap tests that are based on approximately pivotal statistics provide both adjustment of size and enhancement of power. These tests are therefore recommended for use in situations similar to those included in the simulation study.     

嫩模现象：一种新兴青年文化

嫩模现象是个横空出世的新兴青年文化现象，亦是香港普及文化的重要一课。讨论嫩模现象的由来，以及在众声喧哗中隐含的各种文化政治，例如名人概念、青年概念、女性身体等，能检视社会主流论述对此等文化概念的意义转变和规训等。     

美国BIT范本的环境政策考量与变迁及其对中国的启示

美国从1981年启用第一个BIT范本,之后历经数次修订,形成不同版本。其中的环境保护条款从无到有、从简到繁,2012年版本对环境保护又有大力强化。虽然环境例外条款具有法律形态,但因其为缔约方保留环境规制的空间,没有消极影响,其他环境条款尤其专门环境条款则只具有政策形态,对缔约方只有倡导和督促作用,因而也不具有负面意义。基于此,对于中美BIT谈判,中国应该持有像实践WTO规则一样的心态,研究它、接受它,为投身国际实践走出第一步,为将来参与更大范围的规则制定做好准备。     

固定效应部分线性变系数面板模型的快速有效估计

本文将最小二乘支持向量机(LSSVM) 和二次推断函数法(QIF) 相结合，为个体内具有相关结构的固定效应部分线性变系数面板模型提供了一种新的快速估计方法；在一定的正则条件下，论证了参数估计量的渐近正态性和非参数估计量的收敛速度；采用Monte Carlo模拟考察了估计方法在有限样本下的表现并将估计技术应用于现实数据分析。该方法不仅保证了估计的有效性和统计推断力，而且程序运行速度得到较大幅度提升。     

英格兰数理精英教师培养及启示——基于“未来教学学者”计划

英格兰政府针对国内中小学数学和物理等学科专业教师紧缺、学生数理成绩较差的现状，推出了"未来教学学者"（Future Teaching Scholars）精英教师培养计划。这一专项教师培养计划旨在通过严格的选拔标准、系统的培养方案、丰厚的奖学金与助学金以及明确的教师未来职业发展规划，吸引高质量的本科生积极参与，从而提高英格兰数理学科教师的专业水平及学生的数理学科成绩。英格兰政府为改善特定科目和偏远地区学校教师质量而开展的专项教师培养项目为我国相关教师的培养工作提供了积极借鉴：创新教师教育培养模式，提高师范生教学实践能力；充分发挥地方师范院校的主体作用，保障特定地区教师供应；提高师范生选拔标准，促进教师队伍整体质量提升。     

Testing for Serial Independence: Beyond the Portmanteau Approach

Portmanteau tests are typically used to test serial independence even if, by construction, they are generally powerful only in presence of pairwise dependence between lagged variables. In this article, we present a simple statistic defining a new serial independence test, which is able to detect more general forms of dependence. In particular, differently from the Portmanteau tests, the resulting test is powerful also under a dependent process characterized by pairwise independence. A diagram, based on p-values from the proposed test, is introduced to investigate serial dependence. Finally, the effectiveness of the proposal is evaluated in a simulation study and with an application on financial data. Both show that the new test, used in synergy with the existing ones, helps in the identification of the true data-generating process. Supplementary materials for this article are available online.     

Control Chart for Monitoring Autocorrelated Process with Multiple Exogenous Inputs

We propose to use AR-Sieve Bootstrap in the construction of a control chart of an autocorrelated process influenced by multiple exogenous inputs. The control charts are compared with Exponentially Weighted Moving Average (EWMA) control chart through a simulation study. AR-Sieve bootstrap control limits are narrower than EWMA control limits. While the proposed method yields a higher rate of false alarms, it is quick in detecting even minimal structural changes.