Using Latent Variable Modeling for Discrete Time Survival Analysis: Examining the Links of Depression to Mortality

Using a latent variable modeling approach to discrete time survival analysis, the dynamics of the relationships of depression and body mass index to mortality are examined with data from the multiwave, nationally representative Health and Retirement Study. A set of medical and demographic variables are employed as time-invariant covariates along with lag-1 depression scores and body mass indexes as time-varying covariates for mortality within an up to 2-year follow-up interval. The results indicate marked links of immediately prior depression levels, as well as notable relations of the body mass indexes, to within-wave mortality in middle-aged and older adults. The approach highlights the benefits of using latent variable modeling for survival analysis, and its findings represent potentially important relationships of clinical and theoretical relevance.     

数学建模课教学应注意的几个问题

在实际教学过程中,结合当前学生和数学建模这门课程的特点,探索出了几点富有成效的教学方法,对其它高校的建模课的教学有一定的借鉴作用.     

Causal Mediation Analysis With a Binary Outcome and Multiple Continuous or Ordinal Mediators: Simulations and Application to an Alcohol Intervention

We investigate a method to estimate the combined effect of multiple continuous/ordinal mediators on a binary outcome: (a) fit a structural equation model with probit link for the outcome and identity/probit link for continuous/ordinal mediators, (b) predict potential outcome probabilities, and (c) compute natural direct and indirect effects. Step 2 involves rescaling the latent continuous variable underlying the outcome to address residual mediator variance and covariance. We evaluate the estimation of risk-difference- and risk-ratio-based effects (RDs, RRs) using the maximum likelihood (ML), mean-and-variance-adjusted weighted least squares (WLSMV) and Bayes estimators in Mplus. Across most variations in path-coefficient and mediator-residual-correlation signs and strengths, and confounding situations investigated, the method performs well with all estimators, but favors ML/WLSMV for RDs with continuous mediators, and Bayes for RRs with ordinal mediators. Bayes outperforms ML/WLSMV regardless of mediator type when estimating RRs with small potential outcome probabilities and in two other special cases. An adolescent alcohol prevention study is used for illustration.     

高速铣削过程中铣削力的建模

研究了球头铣刀高速铣削过程铣削力建模与仿真。考虑了作用在前、后刀面上的正压力和摩擦力,建立了高速铣削加工中局部铣削力模型,在上述基础上建立了整体铣削力的模型。通过铣削实验,验证了所建模型的正确性。     

Identifying and developing crosscutting environmental education outcomes for adolescents in the twenty-first century (EE21)

Abstract

While multiple valid measures exist for assessing outcomes of environmental education (EE) programs, the field lacks a comprehensive and logistically feasible common instrument that can apply across diverse programs. We describe a participatory effort for identifying and developing crosscutting outcomes for Environmental Education in the twenty-first Century (EE21). Following extensive input and debate from a wide range of EE providers and researchers, we developed, tested and statistically validated crosscutting scales for measuring consensus-based outcomes for individual participants in youth EE programs using confirmatory factor analysis across six unique sites, including two single-day field trip locations, four multiday residential programs and one science museum in the United States. The results suggest that the scales are valid and reliable for measuring outcomes that many EE programs in the United States can aspire to influence in adolescent participants, ages 10–14.     

Course-level modeling of preservice teacher learning of technology integration

We introduce an analytic approach to examine preservice teachers' technology integration learning as a process mapped against their technology-related course experience in a technology integration course. The approach assumes that (1) the preservice teachers have common course learning experience; (2) their data are collected pre- and post-course and paired; (3) the sample size is large enough to generate a structural covariance model; (4) the measurement is contextualized to the course characteristics around the types of technology tasks/tools used in the course and whether or not they were explicitly taught. The approach was applied to 368 preservice teachers' paired data to illustrate how the approach addresses the methodological issue of construct validity in TPACK measures, highlights the importance of technology integration course experience, and provides useful insights into a particular technology integration learning to its stakeholders.     

冲裁模具间隙选择的模糊综合评判

本文的主要目的是讨论在冲裁模具间隙设计时,如何在几种冲裁模具间隙中合理地选出最佳的一种。方法是基于模糊理论,建立了冲裁模具间隙选择的模糊综合评判数学模型,并以冲裁模具间隙选择为例,进行计算说明这种方法的有效性和简便性,创新点是为冲裁模具间隙有效选择提供一种思路与方法。     

Global term weights in distributed environments

This paper examines the estimation of global term weights (such as IDF) in information retrieval scenarios where a global view on the collection is not available. In particular, the two options of either sampling documents or of using a reference corpus independent of the target retrieval collection are compared using standard IR test collections. In addition, the possibility of pruning term lists based on frequency is evaluated.     

金融产品创新绩效之风险作用路径的结构方程模型分析

针对利用调查问卷收集的我国金融产品创新的资料,使用结构方程模型的统计分析方法,考察了开发过程、营销因素、市场环境、组织管理和风险管理等关键风险因素影响创新绩效的风险作用路径和效果,以指导我国金融机构对产品创新风险进行有效控制.