The Game of Contacts: Estimating the Social Visibility of Groups

Estimating the sizes of hard-to-count populations is a challenging and important problem that occurs frequently in social science, public health, and public policy. This problem is particularly pressing in HIV/AIDS research because estimates of the sizes of the most at-risk populations-illicit drug users, men who have sex with men, and sex workers-are needed for designing, evaluating, and funding programs to curb the spread of the disease. A promising new approach in this area is the network scale-up method, which uses information about the personal networks of respondents to make population size estimates. However, if the target population has low social visibility, as is likely to be the case in HIV/AIDS research, scale-up estimates will be too low. In this paper we develop a game-like activity that we call the game of contacts in order to estimate the social visibility of groups, and report results from a study of heavy drug users in Curitiba, Brazil (n = 294). The game produced estimates of social visibility that were consistent with qualitative expectations but of surprising magnitude. Further, a number of checks suggest that the data are high-quality. While motivated by the specific problem of population size estimation, our method could be used by researchers more broadly and adds to long-standing efforts to combine the richness of social network analysis with the power and scale of sample surveys.     

论《卧虎藏龙》的“人文武侠”理想

华裔导演李安的《卧虎藏龙》让西方人重新认识了中国的武侠电影.影片成功的最重要原因,是将武侠电影从感官层面提升到了文化与人文的层面,将武侠与人文关怀兼容并蓄,从而建立一个新型的武侠电影叙事模式.这种“人文武侠”的叙事模式,为中国武侠电影的转型带来了新的范式.     

教育生态学理论指导下的大学英语隐性课程个案研究——以包头师范学院预科生为例

目前,少数民族预科生的英语学习主要困扰有两个方面：首先,由于英语基础差,再加上民族文化的熏陶,预科生整体对英语学习动机及兴趣不浓,缺乏学习英语的自信心;其次,现行英语教材不符合预科生的民族特点及学习要求。在教育生态学理论的指导下,可以从学校校园文化、班级文化、师生关系及教材方面开发预科生英语隐性课程,提高预科生的英语学习兴趣和自信心,改善预科生的整体英语学习水平。     

Extensions of Stein's Lemma for the Skew-Normal Distribution

When two random variables have a bivariate normal distribution, Stein's lemma (Stein, 1973 Stein , C. M. ( 1973 ). Estimation of the mean of a multivariate normal distribution . Proc. Prague Symp. Asymptotic Statist. 345 – 381 . [Google Scholar] 1981 Stein , C. M. ( 1981 ). Estimation of the mean of a multivariate normal distribution . Ann. Statist. 9 : 1135 – 1151 .[Crossref], [Web of Science ®] , [Google Scholar]), provides, under certain regularity conditions, an expression for the covariance of the first variable with a function of the second. An extension of the lemma due to Liu (1994 Liu , J. S. ( 1994 ). Siegel's formula via Stein's identities . Statist. Probab. Lett. 21 : 247 – 251 .[Crossref], [Web of Science ®] , [Google Scholar]) as well as to Stein himself establishes an analogous result for a vector of variables which has a multivariate normal distribution. The extension leads in turn to a generalization of Siegel's (1993 Siegel , A. F. ( 1993 ). A surprising covariance involving the minimum of multivariate normal variables . J. Amer. Statist. Assoc. 88 : 77 – 80 .[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) formula for the covariance of an arbitrary element of a multivariate normal vector with its minimum element. This article describes extensions to Stein's lemma for the case when the vector of random variables has a multivariate skew-normal distribution. The corollaries to the main result include an extension to Siegel's formula. This article was motivated originally by the issue of portfolio selection in finance. Under multivariate normality, the implication of Stein's lemma is that all rational investors will select a portfolio which lies on Markowitz's mean-variance efficient frontier. A consequence of the extension to Stein's lemma is that under multivariate skew-normality, rational investors will select a portfolio which lies on a single mean-variance-skewness efficient hyper-surface.     

节点集重要性测度——综合法及其在知识共享网络中的应用

在具有社会关系结构的经济系统及通讯网络系统等许多现实的系统中,人们经常关注节点集在系统中的重要性问题.在分析如何有效反映网络中节点集重要性的基础上,针对节点赋权网络,利用节点集删除的研究方法,建立节点集重要性的综合测度数学模型;然后,借助于图的距离矩阵的计算方法设计该模型的算法;最后,给出该方法在知识共享网中的应用.