Bayesian Variable Selection Under Collinearity

In this article, we highlight some interesting facts about Bayesian variable selection methods for linear regression models in settings where the design matrix exhibits strong collinearity. We first demonstrate via real data analysis and simulation studies that summaries of the posterior distribution based on marginal and joint distributions may give conflicting results for assessing the importance of strongly correlated covariates. The natural question is which one should be used in practice. The simulation studies suggest that posterior inclusion probabilities and Bayes factors that evaluate the importance of correlated covariates jointly are more appropriate, and some priors may be more adversely affected in such a setting. To obtain a better understanding behind the phenomenon, we study some toy examples with Zellner’s g-prior. The results show that strong collinearity may lead to a multimodal posterior distribution over models, in which joint summaries are more appropriate than marginal summaries. Thus, we recommend a routine examination of the correlation matrix and calculation of the joint inclusion probabilities for correlated covariates, in addition to marginal inclusion probabilities, for assessing the importance of covariates in Bayesian variable selection.     

Unit Root Tests in the Presence of Multi-Variance Break and Level Shifts That Have Power Against the Piecewise Stationary Alternative

Structural breaks in the level as well as in the volatility have often been exhibited in economic time series. In this paper, we propose new unit root tests when a time series has multiple shifts in its level and the corresponding volatility. The proposed tests are Lagrangian multiplier type tests based on the residual's marginal likelihood which is free from the nuisance mean parameters. The limiting null distributions of the proposed tests are the χ²distributions, and are affected not by the size and the location of breaks but only by the number of breaks.

We set the structural breaks under both the null and the alternative hypotheses to relieve a possible vagueness in interpreting test results in empirical work. The null hypothesis implies a unit root process with level shifts and the alternative connotes a stationary process with level shifts. The Monte Carlo simulation shows that our tests are locally more powerful than the OLSE-based tests, and that the powers of our tests, in a fixed time span, remain stable regardless the number of breaks. In our application, we employ the data which are analyzed by Perron (1990), and some results differ from those of Perron's (1990).     

Assessment of modeling longitudinal binary data based on graphical methods

Longitudinal categorical data are commonly applied in a variety of fields and are frequently analyzed by generalized estimating equation (GEE) method. Prior to making further inference based on the GEE model, the assessment of model fit is crucial. Graphical techniques have long been in widespread use for assessing the model adequacy. We develop alternative graphical approaches utilizing plots of marginal model-checking condition and local mean deviance to assess the GEE model with logit link for longitudinal binary responses. The applications of the proposed procedures are illustrated through two longitudinal binary datasets.     

TWO-PASS CUSUM TO IDENTIFY AGE-CLUSTER OUTBREAKS

The paper introduces a two-pass adaptive cumulative sum (CUSUM) statistic to identify age clusters (age grouping) that significantly contribute to epidemics or unusually high counts. If epidemiologists know that an epidemic is confined to a narrow age group, then this information not only makes it clear where to target the epidemiological effort but also helps them decide whether to respond. It is much easier to control an epidemic that starts in a narrow age range of the population, such as pre-school children, than an epidemic that is not confined demographically or geographically.     

我国“刘易斯转折点”的测定及其对策研究

“刘易斯转折点”是我国社会经济发展的重要时点。这里通过估算得出．我国将在2013年左右越过了“刘易斯第一转折点”,在2026年左右迎来“刘易斯第二转折点”。而要顺利地跨越“刘易斯转折点”．转变我国经济发展方式才是惟一出路。     

新经济时代我国城市规划的几个问题的讨论

随着新经济现象的迅速涌现,新经济时代已经来临,在这种形式下,我国新的一轮城市规划正在面临新的挑战。如正在许多大城市周边形成的边缘城市现象、城市信息化、全球经济一体化以及区域合作的兴起等都深刻地影响着城市以及区域的发展,城市规划作为政府宏观调控的重要手段,如何在其中发挥重要的促进作用等都值得进一步的探讨。     

再论罪名变更的法理基础及其模式选择--刑事一体化角度的思考

在法院能否变更起诉指控的罪名以及如何变更起诉指控罪名的问题上,一些国家和地区存在着立法上的差别和理论上的分野.我国目前在程序设计上对法院的罪名变更权缺乏制约,理论界提出的种种改革方案也都值得商榷.我国罪名变更制度的建构,应当立足于我国特有的法文化传承和法治土壤,应当建立以四要件犯罪构成模式为基石并与诉因制度相整合的"诉因制度本土化"模式.     

藏彝走廊边缘群体的主体性表达——羌寨罗达的文化意义

多族群地区中,族群文化互动是一个客观事实,也是人类学研究的经典话题,探讨文化互动中边缘群体的主体性则是新近人类学关注的主题之一。在藏彝走廊地区,羌族在吸收藏族的罗达后,根据自身社会结构、信仰和认知方式对罗达进行了积极的生产和维持。这是一个文化经营的过程,它体现了身处边缘状态的羌族利用自身观念和价值创造文化与保持身份认同的主体能动性。探讨边缘群体的主体性表达有助于深化和拓展华夏边缘论,超越中心与边缘的对立,同时也有利于思考全球化时代地方     

我国工业污染物的影子价格估计

 污染物的影子价格体现了污染物的边际减排成本。本文采用二次型方向性距离函数和 2003-2008年我国284个地级及以上城市工业部门数据,对废水、SO2和烟尘等三种污染物的影子价格进行了估计。结果发现,2003-2008年期间,废水、SO2、烟尘的影子价格或边际减排成本分别为0.0178万元/吨、5.158万元/吨和4.597万元/吨。SO2排污权交易价格相比污染减排成本偏低,影响了排污权交易市场的有效运作。污染物的影子价格在不同城市具有较大差异,这种差异性能够在一定程度上被污染排放规模、监管强度和污染治理的规模经济性等因素所解释。     

Test of parameter changes in a class of observation-driven models for count time series

Abstract

This paper investigates the parameter-change tests for a class of observation-driven models for count time series. We propose two cumulative sum (CUSUM) test procedures for detection of changes in model parameters. Under regularity conditions, the asymptotic null distributions of the test statistics are established. In addition, the integer-valued generalized autoregressive conditional heteroskedastic (INGARCH) processes with conditional negative binomial distributions are investigated. The developed techniques are examined through simulation studies and also are illustrated using an empirical example.