Multivariate meta-analysis: the effect of ignoring within-study correlation

Summary.  Multivariate meta-analysis allows the joint synthesis of summary estimates from multiple end points and accounts for their within-study and between-study correlation. Yet practitioners usually meta-analyse each end point independently. I examine the role of within-study correlation in multivariate meta-analysis, to elicit the consequences of ignoring it. Using analytic reasoning and a simulation study, the within-study correlation is shown to influence the 'borrowing of strength' across end points, and wrongly ignoring it gives meta-analysis results with generally inferior statistical properties; for example, on average it increases the mean-square error and standard error of pooled estimates, and for non-ignorable missing data it increases their bias. The influence of within-study correlation is only negligible when the within-study variation is small relative to the between-study variation, or when very small differences exist across studies in the within-study covariance matrices. The findings are demonstrated by applied examples within medicine, dentistry and education. Meta-analysts are thus encouraged to account for the correlation between end points. To facilitate this, I conclude by reviewing options for multivariate meta-analysis when within-study correlations are unknown; these include obtaining individual patient data, using external information, performing sensitivity analyses and using alternatively parameterized models.     

二元Jackson型算子的最佳逼近常数

研究了二元Jackson多项式对周期函数的逼近阶估计.分别给出了以一阶和二阶光滑模刻画的Jackson型估计式,并分别给出了逼近的最佳常数.     

Finite mixtures approach to ecological regression

During past few years great attention has been devoted to the analysis of disease incidence and mortality rates, with an explicit focus on modelling geographical variation of rates observed in spatially adjacent regions. The general aim of these contributes has been both to highlight clusters of regions with homogeneous relative risk and to determine the effects of observed and unobserved risk factors related to the analyzed disease. Most of the proposed modelling approaches can be derived as alternative specifications of the components of a general convolution model (Molliè, 1996). In this paper, we consider the semiparametric approach discussed by Schlattmann and Böhning (1993); in particular, we focus on models with an explicit spatially structured component (see Biggeri et al., 2000), and propose alternative choices for the structure of the spatial component.     

求常系数非齐次微分方程特解的一种新方法--特征多项式法

提出了求解常系数非齐次线性微分方程特解的一种新简化方法——特征多项式法，它比通常教材介绍的两种传统方法——比较系数法和拉普拉斯变换法简捷，对高阶、项数多的微分方程显得更有意义。     

试论细致平衡、质量守恒在化学动力学中的应用--从细致平衡、质量守恒看速率常数和平衡常数及基元反应总反应的关系

依据细致平衡原理、质量守恒原理来推导基元反应的速率常数和总反应的化学平衡常数的关系以及基元反应总反应的关系     

美国政府外交政策同质性研究——以布什和奥巴马两届政府外交政策为例

美国是当今世界唯一的超级大国,国际影响力无与伦比,对美国外交政策的研究具有重要现实意义。在美国外交史上,历届总统都会适时提出自己的外交理念和外交政策,但无论美国哪个总统上台,其外交政策虽有不同,但都受到支配美国外交决策制定的五大基本恒律的制约,有着同质性趋向。对奥巴马和布什政府外交政策的比较研究,可以使我们更好地认识美国外交政策的实质。     

Run rules based phase II c and np charts when process parameters are unknown

Abstract

The performance of attributes control charts is usually evaluated under the assumption of known process parameters (i.e., the nominal proportion of non conforming units or the nominal average number of nonconformities). However, in practice, these process parameters are rarely known and have to be estimated from an in-control Phase I data set. The major contributions of this paper are (a) the derivation of the run length properties of the Run Rules Phase II c and np charts with estimated parameters, particularly focusing on the ARL, SDRL, and 0.05, 0.5, and 0.95 quantiles of the run length distribution; (b) the investigation of the number m of Phase I samples that is needed by these charts in order to obtain similar in-control ARLs to the known parameters case; and (c) the proposition of new specific chart parameters that allow these charts to have approximately the same in-control ARLs as the ones obtained in the known parameters case.     

Steady-state behaviour of serial queueing processes with impatient customers

This paper considers the steady-state behaviour of serial queueing processes with impatient customers having random selection for service, Poisson arrivals and exponential service times where the waiting space is infinite as well as finite. The expressions for the steady-state solution and mean queue length have been derived whenever the queue-discipline is first-come,first-served     

Efficient Bayesian inference for exponential random graph models by correcting the pseudo-posterior distribution

Exponential random graph models are an important tool in the statistical analysis of data. However, Bayesian parameter estimation for these models is extremely challenging, since evaluation of the posterior distribution typically involves the calculation of an intractable normalizing constant. This barrier motivates the consideration of tractable approximations to the likelihood function, such as the pseudolikelihood function, which offers an approach to constructing such an approximation. Naive implementation of what we term a pseudo-posterior resulting from replacing the likelihood function in the posterior distribution by the pseudolikelihood is likely to give misleading inferences. We provide practical guidelines to correct a sample from such a pseudo-posterior distribution so that it is approximately distributed from the target posterior distribution and discuss the computational and statistical efficiency that result from this approach. We illustrate our methodology through the analysis of real-world graphs. Comparisons against the approximate exchange algorithm of Caimo and Friel (2011) are provided, followed by concluding remarks.     

近地面光学湍流估算与测量

根据Monin-Obkhov相似理论,建立了近地面大气估算和预测模型,并进行了数值分析。与其他基于相似理论的估算模型对比结果表明,在不稳定条件下利用气象要素和一些经验参数估算近地面平坦地形光学湍流,理论估计和实验结果符合较好,在低风速时折射率结构常数随风速增加而减小。利用Thiermann-Kohnle模型,结合地理位置和太阳辐射规律,预测了某地某时段的光学湍流,并通过实地测量气象数据估测了折射率结构常数和湍流内尺度。