Controlled Direct and Mediated Effects: Definition,Identification and Bounds

Abstract. Results are given which provide bounds for controlled direct effects when nounmeasured confounding assumptions required for the identification of these effects do not hold. Previous results concerning bounds for controlled direct effects rely on monotonicity relationships between the treatment, mediator and the outcome themselves; the results presented in this article instead assume that monotonicity relationships hold between the unmeasured confounding variable or variables and the treatment, mediator and outcome. Whereas prior results give bounds that contain the null hypothesis of no direct effect, the results presented here will in many instances yield bounds that do not contain the null hypothesis of no direct effect. For contexts in which a set of variables intercepts all paths between a treatment and an outcome, it is possible to provide a definition for a controlled mediated effect. We discuss the identification of these controlled mediated effects; the bounds for controlled direct effects are applicable also to controlled mediated effects. An example is given to illustrate how the results in the article can be used to draw inferences about direct and mediated effects in the presence of unmeasured confounding variables.     

Use of prior information for estimating the variance components

The MINQUE and its modifications are considered for estimating the variances of the balanced one-way random effects model. The effects of the a priori values on the estimators of the variances are examined in detail. The Mean Square Errors of the estimators are compared for variations in the prior values of the unknown variances.     

李渔剧论的观众立场及其贡献

本文以为李渔戏剧理论的中心是观众 ,围绕观众来探讨剧本的创作、演出、戏剧的功能及其发展等是李渔剧论的最大特色。文章指出 :李渔从观众立场出发提出了“机趣”的戏剧功能观 ,并揭示了观众对戏剧艺术发展负有不可推卸的责任。     

兼并效应与产品覆盖策略

在行业寡头垄断竞争中, 引入产品覆盖策略竞争的变量, 把企业兼并时的竞争假定为两 个阶段两种变量: 先是产品覆盖策略竞争, 后是产品产量竞争, 并设计了一个描述这种兼并竞 争的模型. 在此基础上, 分析了参与和未参与兼并的企业的产品覆盖策略变化对各企业利润和 价格的影响, 在一定程度上解释了兼并悖论. 我们赞成适度的兼并控制政策, 但在经济萧条时 期可适当放宽.     

Residential Building Codes,Affordability, and Health Protection: A Risk-Tradeoff Approach

Residential building codes intended to promote health and safety may produce unintended countervailing risks by adding to the cost of construction. Higher construction costs increase the price of new homes and may increase health and safety risks through income and stock effects. The income effect arises because households that purchase a new home have less income remaining for spending on other goods that contribute to health and safety. The stock effect arises because suppression of new-home construction leads to slower replacement of less safe housing units. These countervailing risks are not presently considered in code debates. We demonstrate the feasibility of estimating the approximate magnitude of countervailing risks by combining the income effect with three relatively well understood and significant home-health risks. We estimate that a code change that increases the nationwide cost of constructing and maintaining homes by $150 (0.1% of the average cost to build a single-family home) would induce offsetting risks yielding between 2 and 60 premature fatalities or, including morbidity effects, between 20 and 800 lost quality-adjusted life years (both discounted at 3%) each year the code provision remains in effect. To provide a net health benefit, the code change would need to reduce risk by at least this amount. Future research should refine these estimates, incorporate quantitative uncertainty analysis, and apply a full risk-tradeoff approach to real-world case studies of proposed code changes.     

Some practical issues in the evaluation of heterogeneous labour market programmes by matching methods

Summary.  Recently several studies have analysed active labour market policies by using a recently proposed matching estimator for multiple programmes. Since there is only very limited practical experience with this estimator, this paper checks its sensitivity with respect to issues that are of practical importance in this kind of evaluation study. The estimator turns out to be fairly robust to several features that concern its implementation. Furthermore, the paper demonstrates that the matching approach per se is no panacea for solving all the problems of evaluation studies, but that its success depends critically on the information that is available in the data. Finally, a comparison with a bootstrap distribution provides some justification for using a simplified approximation of the distribution of the estimator that ignores its sequential nature.     

Covariates and Random Effects in a Gamma Process Model with Application to Degradation and Failure

The gamma process is a natural model for degradation processes in which deterioration is supposed to take place gradually over time in a sequence of tiny increments. When units or individuals are observed over time it is often apparent that they degrade at different rates, even though no differences in treatment or environment are present. Thus, in applying gamma-process models to such data, it is necessary to allow for such unexplained differences. In the present paper this is accomplished by constructing a tractable gamma-process model incorporating a random effect. The model is fitted to some data on crack growth and corresponding goodness-of-fit tests are carried out. Prediction calculations for failure times defined in terms of degradation level passages are developed and illustrated.     

“以学生为中心的主题教学模式”实验研究

通过“以学生为中心的主题教学模式”教改实验测试成绩数据和一系列调查结果的比较分析 ,说明了教学改革对于大学英语课堂教学的效果和学生学习能力的培养有着十分重要的作用     

Covariate Order Tests for Covariate Effect

A new approach for constructing tests for association between a random right censored life time variable and a covariate is proposed. The basic idea is to first arrange the observations in increasing order of the covariate and then base the test on a certain point process defined by the observation times. Tests constructed by this approach are robust against outliers in the covariate values or misspecification of the covariate scale since they only use the ordering of the covariate. Of particular interest is a test based on the Anderson-Darling statistic. This test has good power properties both against monotonic and nonmonotonic dependencies between the covariate and the life time variable.     

“意见领袖”新探

20世纪40年代,美国哥伦比亚大学的传播学者保罗·拉扎斯费尔德提出了"意见领袖"的概念,他认为:对于媒介所播的信息和观点,有部分受众会积极接受,并加以再传播,这些人即为"意见领袖";而另一部分人则主要依靠与这些"意见领袖"的接触来指导自己的行动。今天重新起用"意见领袖"这一概念,旨在论析媒体能够反映、影响、组织社会舆论,以取得社会思潮与情绪的统一化,使社会公众遵循既定的社会规范与社会目标,从而真正实现新闻传播引导舆论的社会职能。