Variability explained by covariates in linear mixed‐effect models for longitudinal data

Variability explained by covariates or explained variance is a well‐known concept in assessing the importance of covariates for dependent outcomes. In this paper we study R² statistics of explained variance pertinent to longitudinal data under linear mixed‐effect models, where the R² statistics are computed at two different levels to measure, respectively, within‐ and between‐subject variabilities explained by the covariates. By deriving the limits of R² statistics, we find that the interpretation of explained variance for the existing R² statistics is clear only in the case where the covariance matrix of the outcome vector is compound symmetric. Two new R² statistics are proposed to address the effect of time‐dependent covariate means. In the general case where the outcome covariance matrix is not compound symmetric, we introduce the concept of compound symmetry projection and use it to define level‐one and level‐two R² statistics. Numerical results are provided to support the theoretical findings and demonstrate the performance of the R² statistics. The Canadian Journal of Statistics 38: 352–368; 2010 © 2010 Statistical Society of Canada     

The Tale of Cochran's Rule: My Contingency Table has so Many Expected Values Smaller than 5, What Am I to Do?

In an informal way, some dilemmas in connection with hypothesis testing in contingency tables are discussed. The body of the article concerns the numerical evaluation of Cochran's Rule about the minimum expected value in r × c contingency tables with fixed margins when testing independence with Pearson's X² statistic using the χ² distribution.     

Lack-of-fit testing of a regression model with response missing at random

This paper proposes a class of lack-of-fit tests for fitting a linear regression model when some response variables are missing at random. These tests are based on a class of minimum integrated square distances between a kernel type estimator of a regression function and the parametric regression function being fitted. These tests are shown to be consistent against a large class of fixed alternatives. The corresponding test statistics are shown to have asymptotic normal distributions under null hypothesis and a class of nonparametric local alternatives. Some simulation results are also presented.     

Addition of runs to an s-level supersaturated design

The purpose of the present work is to extend the work of Gupta et al. (2010) to s  -level column balanced supersaturated designs. Addition of runs to an existing E(χ²)-optimal$E({\chi }^2)\mathrm{-}\mathrm{optimal}$ supersaturated design and to study the optimality of the resulting design is an important issue. This paper considers the study of the optimality of the resulting design. A lower bound to E(χ²)$E({\chi }^2)$ has been obtained for the extended supersaturated designs. Some examples and a small catalogue of E(χ²)-optimal$E({\chi }^2)\mathrm{-}\mathrm{optimal}$ supersaturated designs are also presented.     

对外贸易隐含SO2测算及影响因素的结构分解分析

 本研究根据中国2002、2005、2007年非竞争型投入产出表、OECD的国外投入产出表和GTAP Version 7.0的SO2排放强度等数据,利用多国投入产出模型方法测算了中国对外贸易中隐含SO2,相关的行业结构分布以及隐含污染物在主要贸易伙伴国的贸易流向,并通过结构分解方法分析了三大因素对出口贸易隐污染物的贡献大小。研究结果表明：2002年至2007年间,我国对外贸易创造了巨大贸易顺差,同时也带来了大量隐含SO2顺差;迅速增长的贸易规模是出口贸易隐含污染物增加的主要因素,但是,环境保护和节能减排技术改进导致的SO2排放强度下降抑制出口贸易隐含SO2增加,而投入产出中间结构变化对其影响较小。     

B2C网站设计因素与初始信任关系的实证研究

通过实证探索并验证了网站结构、网站内容和视觉效果对消费者初始信任的影响,同时还验证了社会存在感在其中所起的中介作用.研究结果发现:网站结构和网站内容对消费者初始信任有着直接的积极影响,社会存在感在其中承担着部分中介作用;网站视觉效果对消费者初始信任的影响虽不显著,但却对社会存在感有着显著的影响.     

Who is bullying whom in ethnically diverse primary schools? Exploring links between bullying,ethnicity, and ethnic diversity in Dutch primary schools

This study investigated associations between ethnicity, ethnic diversity, and bullying among 739 pupils enrolled in their last year of primary school. Hypotheses derived from social misfit and inter-ethnic relations theories were tested using the multilevel p₂ model. Our key findings were: (1) inter- and intra-ethnic bullying are just as common in ethnically heterogeneous as in homogeneous classes; (2) pupils belonging to the Turkish and Moroccan minority groups bully significantly more than native Dutch (in particular according to victims); the chance to be victimized does not depend on the ethnic background of the pupil; (3) the prevalence of inter- and intra-ethnic bullying depends on the level of ethnic diversity in the class; inter-ethnic and intra-ethnic bullying increase with increasing levels of ethnic diversity.     

骨肽对成骨细胞骨形成蛋白2表达影响的实验研究

目的 研究骨肽对成骨细胞骨形成蛋白2（BMP2）表达影响.方法 体外分离培养成骨细胞,0.02mg/ml,0.08mg/ml,0.32mg/ml三个剂量浓度骨肽分别作用24小时,应用流式细胞术检测成骨细胞增殖情况.以上三个剂量浓度骨肽再分别作用成骨细胞24小时、48小时、72小时,收集细胞上清利用酶联免疫法（ELISA法）检测BMP2表达含量.结果 三个尽剂量浓度作用24小时均可引起成骨细胞增殖,并存在剂量依赖性.骨肽各浓度组在24小时、48小时均可引起BMP2表达增高,其中0.08mg/ml剂量组作用48小时效果最为显著.结论 骨肽可促进成骨细胞BMP2蛋白表达,从而发挥促进成骨细胞增殖和分化的作用.     

带根近二正则平面地图的数目

文章讨论带根近二正则平面地图的计数,给出组合不同的以根面次、非根点数和内面数为参数的带根近二正则平面地图的数目,其中有一个是无和式.     

碳排放配额分配的DEA建模与应用

在区域层面分解CO2排放强度下降目标是我国能源经济政策关注的热点问题,也是实现国家“十二五”CO2排放强度削减目标的有效途径.基于数据包络分析方法(DEA),提出一种新的DEA-CEA(DEA based carbon emissions allocation)配额分配模型,该模型将CO2排放配额分配问题视为一种总量受控的资源配置问题,以效率优先为目标,人均公平为约束,将国家排放总量分配给各省.采用2010年数据,基于传统DEA分配模型和DEA-CEA模型分别进行计算,并与2010年实际情况进行对比分析,结果显示:在相同生产水平和减排约束下,DEA-CEA模型分配结果的减排成本更低,减排任务更符合各地区实际情况,从而更有利于地区经济协调发展,地区间分配配额的差距有所减小进而有助于提高减排政策的可执行性.