Product-limit survival functions with correlated survival times

A simple variance estimator for product-limit survival functions is demonstrated for survival times with nested errors. Such data arise whenever survival times are observed within clusters of related observations. Greenwood's formula, which assumes independent observations, is not appropriate in this situation. A robust variance estimator is developed using Taylor series linearized values and the between-cluster variance estimator commonly used in multi-stage sample surveys. A simulation study shows that the between-cluster variance estimator is approximately unbiased and yields confidence intervals that maintain the nominal level for several patterns of correlated survival times. The simulation study also shows that Greenwood's formula underestimates the variance when the survival times are positively correlated within a cluster and yields confidence intervals that are too narrow. Extension to life table methods is also discussed.     

一只披着中国外衣的美国熊猫——《功夫熊猫》阿宝的文化身份解读

好莱坞先后两部《功夫熊猫》的上映引发了中国观众的热议,其中主人公阿宝的文化身份问题更是争议的焦点。本研究首先分析了影片中蕴含的中国元素,然后分别从颠覆"熊猫"的符号、"个人主义"的"美国梦"、"命中注定"的"速成超人"、遭遇和解决身份危机、"正义战胜邪恶"的主题模式以及惊险而幽默的好莱坞式风格等方面阐释了片中所折射出的美国文化价值观,旨在说明阿宝实质上是一只披着中国外衣的美国熊猫。     

论费耶阿本德的“怎么都行”

费耶阿本德从批判传统的理性主义方法论出发,通过对科学史的考察,提出了＂怎么都行＂的多元主义方法论。不过,费耶阿本德的＂反对方法＂并不是反对一切方法,他的＂怎么都行＂也不是一条新的方法论规则。＂怎么都行＂的多元主义方法论有很多值得人们借鉴的地方,也存在一些偏颇之处,需要正确地加以理解。     

Sharpening Jensen's Inequality

This article proposes a new sharpened version of Jensen's inequality. The proposed new bound is simple and insightful, is broadly applicable by imposing minimum assumptions, and provides fairly accurate results in spite of its simple form. Applications to the moment generating function, power mean inequalities, and Rao-Blackwell estimation are presented. This presentation can be incorporated in any calculus-based statistical course.     

Predictive Influence of Unavailable Values of Future Explanatory Variables in a Linear Model

We consider an approach to prediction in linear model when values of the future explanatory variables are unavailable, we predict a future response y ^f at a future sample point x ^f when some components of x ^f are unavailable. We consider both the cases where x ^f are dependent and independent but normally distributed. A Taylor expansion is used to derive an approximation to the predictive density, and the influence of missing future explanatory variables (the loss or discrepancy) is assessed using the Kullback–Leibler measure of divergence. This discrepancy is compared in different scenarios including the situation where the missing variables are dropped entirely.     

Variable selection approach for zero-inflated count data via adaptive lasso

This article proposes a variable selection approach for zero-inflated count data analysis based on the adaptive lasso technique. Two models including the zero-inflated Poisson and the zero-inflated negative binomial are investigated. An efficient algorithm is used to minimize the penalized log-likelihood function in an approximate manner. Both the generalized cross-validation and Bayesian information criterion procedures are employed to determine the optimal tuning parameter, and a consistent sandwich formula of standard errors for nonzero estimates is given based on local quadratic approximation. We evaluate the performance of the proposed adaptive lasso approach through extensive simulation studies, and apply it to analyze real-life data about doctor visits.     

论加拿大华裔作家余兆昌的儿童文学创作

余兆昌(Paul Yee)是加拿大著名华裔英文儿童文学作家,其创作的儿童文学作品,以儿童为本位,集中表现华人历史,自觉立足华人立场,为加拿大华人的权利和主张发声,具有强烈的华人意识。在形式上,余兆昌创作的儿童文学作品,带入了众多的中国民间风俗文化因素,注入了强烈的情感力量,形成了以第三人称全知客观叙事为主的叙述角度和简洁平实却富有变化的文字风格,具有融现代性、故事性、幻想性、成长性、趣味性、朴素性为一体的特点。     

Calibrated imputation in surveys under a quasi-model-assisted approach

Summary.  We propose to use calibrated imputation to compensate for missing values. This technique consists of finding final imputed values that are as close as possible to preliminary imputed values and are calibrated to satisfy constraints. Preliminary imputed values, potentially justified by an imputation model, are obtained through deterministic single imputation. Using appropriate constraints, the resulting imputed estimator is asymptotically unbiased for estimation of linear population parameters such as domain totals. A quasi-model-assisted approach is considered in the sense that inferences do not depend on the validity of an imputation model and are made with respect to the sampling design and a non-response model. An imputation model may still be used to generate imputed values and thus to improve the efficiency of the imputed estimator. This approach has the characteristic of handling naturally the situation where more than one imputation method is used owing to missing values in the variables that are used to obtain imputed values. We use the Taylor linearization technique to obtain a variance estimator under a general non-response model. For the logistic non-response model, we show that ignoring the effect of estimating the non-response model parameters leads to overestimating the variance of the imputed estimator. In practice, the overestimation is expected to be moderate or even negligible, as shown in a simulation study.     

“新经济人”:科学管理的本质——“新经济”下对泰罗“经济人”假设的思考

学术界普遍认为 :泰罗的科学管理是以纯粹的“古典经济人”为其人性假设。这种看法其实是对泰罗的误解。泰罗的“经济人”假设体现了物质刺激与精神刺激 ,外在刺激与内在刺激的结合 ;制度管理与文化管理 ,刚性管理与柔性管理的统一 ;硬环境与软环境 ,有形环境与无形环境的融合 ,蕴含着丰富的“社会人”、“自我实现人”的思想 ,本质上已区别于以往时代的“古典经济人”,成为“新经济人”。     

Longitudinal analysis of friendship networks

This note discusses and demonstrates methods, both exploratory and confirmatory, for analysing data from friendship networks collected over time. The focus is on stochastic models for dyadic interaction designed to quantify the structural effect of reciprocity on arc changes. The networks studied were previously analysed by Hallinan (Social Networks 1: 193–210) who was concerned with stability of dyadic choices and the direction of change of asymmetric dyads to either mutual or null dyads. These aspects of the networks are really of secondary importance to the effect of reciprocated choices on the probabilities of dyadic change. Measures of this ‘reciprocity effect’ are presented, and comments on the rationale for continuous-time Markov chains as models for networks are given.