Multiple-bias modelling for analysis of observational data

Summary.  Conventional analytic results do not reflect any source of uncertainty other than random error, and as a result readers must rely on informal judgments regarding the effect of possible biases. When standard errors are small these judgments often fail to capture sources of uncertainty and their interactions adequately. Multiple-bias models provide alternatives that allow one systematically to integrate major sources of uncertainty, and thus to provide better input to research planning and policy analysis. Typically, the bias parameters in the model are not identified by the analysis data and so the results depend completely on priors for those parameters. A Bayesian analysis is then natural, but several alternatives based on sensitivity analysis have appeared in the risk assessment and epidemiologic literature. Under some circumstances these methods approximate a Bayesian analysis and can be modified to do so even better. These points are illustrated with a pooled analysis of case–control studies of residential magnetic field exposure and childhood leukaemia, which highlights the diminishing value of conventional studies conducted after the early 1990s. It is argued that multiple-bias modelling should become part of the core training of anyone who will be entrusted with the analysis of observational data, and should become standard procedure when random error is not the only important source of uncertainty (as in meta-analysis and pooled analysis).     

混凝土损伤的非线性细观统计模型

本文利用概率统计的方法，把以体积应变定义的混凝土损伤非线性变形用随机分布裂缝的几何特征尺寸形式给出，并以界面位移跃度解作为对结合缝开裂的描述。计算表明。由于该模型接近混凝土实际结构，对混凝土非线性的描述也具有相当的精度。     

ROBUST ESTIMATION AND HYPOTHESIS TESTS FOR FIRST-ORDER THRESHOLD AUTOREGRESSIVE MODELS

Results of Petrucelli & Woolford (1984) for a first-order threshold autoregressive model are considered from a robust point of view. Robust estimators of the threshold parameters of the model are obtained and their asymptotic normality is proved. Testing the equality of the threshold parameters is considered using the robust analogues of Wald and score test statistics. Limiting distributions of these statistics are given under both null and alternative hypotheses.     

不同因素对体育教育专业学生抑郁检出率的影响

目的：探讨体育教育专业大学生抑郁症状及不同因素对其抑郁检出率的影响．方法：采用贝克抑郁量表进行问卷调查,数据处理采用SPSS19,0和x2检验进行统计分析．结果：抑郁的平均得分12．88±8．60,检出率34．83％;性别、母亲文化程度、家庭经济收入、不良生活事件、身体素质、疾病、学习成绩、人际关系、学习压力,对抑郁的检出率影响差异显著．结论：体育教育专业大学生的抑郁不专属任何特定群体,是多种因素共同作用的结果;运动对大学生抑郁倾向的改善具有积极地作用,但抑郁高得分值,要求对体育教育专业大学生的心理保健工作引起足够重视．     

1998-2000年CAJ-CD收录我校理工类学术论文的统计分析

统计了1998-2000年被CAJ-CD收录的我校作者的理工类学术论文情况,从发文数量、覆盖学科范围以及发文所在期刊、作者分布情况进行了分析,为我校科研发展和专业设置提供了决策依据.     

明代人口之谜探析

"明代户口之雾"一直困扰着后世学者,使人们难以看清明代人口的真实数字,由于当时史书均没有注明所统计户口是否包括男口和女口,所以,给后世学者带来诸多疑问.由于明代人口数一直没有定论,故现代人在著作中都将正史中所记载人口数作为全部人口数引用.通过对户口统计及记载资料的分析可证,明代户口统计是只计男口,不计女口,按自然生殖法则推算,明代人口数要比正史记载的多一倍左右.     

ON CHARACTERIZING DISTRIBUTIONS VIA LINEARITY OF REGRESSION FOR ORDER STATISTICS

Let X₁X_n be a random sample from an absolutely continuous distribution with the corresponding order statistics X_1:n≤X_2:n≤X_n:n. A complete solution of the problem, posed in 1967 by T. Ferguson, of determining the distribution by linearity of regression of X_k+2:n with respect to X_k:n is given. The only possible distributions are of the exponential, power and Pareto type. A linear regression relation for exponents of order statistics is also considered.     

Procrustes Shape Analysis of Planar Point Subsets

Consider a set of points in the plane randomly perturbed about a mean configuration by Gaussian errors. In this paper a Procrustes statistic based on the shapes of subsets of the points is studied, and its approximate distribution is found for small variations. We derive various properties of the distribution including the first two moments, a central limit result and a scaled χ²–-approximation. We concentrate on the independent isotropic Gaussian error case, although the results are valid for general covariance structures. We investigate triangle subsets in detail and in particular the situation where the population mean is regular (i.e. a Delaunay triangulation of the mean of the process is comprised of equilateral triangles of the same size). We examine the variance of the statistic for differently shaped regions and provide an asymptotic result for general shaped regions. The results are applied to an investigation of regularity in human muscle fibre cross-sections.     

Output-sensitive algorithms for Tukey depth and related problems

The Tukey depth (Proceedings of the International Congress of Mathematicians, vol. 2, pp. 523–531, 1975) of a point p with respect to a finite set S of points is the minimum number of elements of S contained in any closed halfspace that contains p. Algorithms for computing the Tukey depth of a point in various dimensions are considered. The running times of these algorithms depend on the value of the output, making them suited to situations, such as outlier removal, where the value of the output is typically small. This research was partly funded by the NSERC Canada.     

When does the expectation of a ratio equal the ratio of expectations?

In this paper we investigate the behaviour of a ratio of random variables and try to find conditions under which, this expectation equals the ratio of expectations.