Asymptotic bias in the linear mixed effects model under non-ignorable missing data mechanisms

Summary.  In longitudinal studies, missingness of data is often an unavoidable problem. Estimators from the linear mixed effects model assume that missing data are missing at random. However, estimators are biased when this assumption is not met. In the paper, theoretical results for the asymptotic bias are established under non-ignorable drop-out, drop-in and other missing data patterns. The asymptotic bias is large when the drop-out subjects have only one or no observation, especially for slope-related parameters of the linear mixed effects model. In the drop-in case, intercept-related parameter estimators show substantial asymptotic bias when subjects enter late in the study. Eight other missing data patterns are considered and these produce asymptotic biases of a variety of magnitudes.     

Bootstrap methods for bias correction and confidence interval estimation for nonlinear quantile regression of longitudinal data

This paper examines the use of bootstrapping for bias correction and calculation of confidence intervals (CIs) for a weighted nonlinear quantile regression estimator adjusted to the case of longitudinal data. Different weights and types of CIs are used and compared by computer simulation using a logistic growth function and error terms following an AR(1) model. The results indicate that bias correction reduces the bias of a point estimator but fails for CI calculations. A bootstrap percentile method and a normal approximation method perform well for two weights when used without bias correction. Taking both coverage and lengths of CIs into consideration, a non-bias-corrected percentile method with an unweighted estimator performs best.     

Some new constructions of circular balanced repeated measurements designs

Repeated measurements designs are widely used in medicine, pharmacology, animal sciences, and psychology. In this article, some infinite series are developed to generate the balanced repeated measurements designs for p (periods) even. For p odd, construction procedures are also described. Catalogues of the proposed designs are also presented for p = 5, 7, 9, when v ≤ 100.     

A comparison study on modeling of clustered and overdispersed count data for multiple comparisons

Data collected in various scientific fields are count data. One way to analyze such data is to compare the individual levels of the factor treatment using multiple comparisons. However, the measured individuals are often clustered – e.g. according to litter or rearing. This must be considered when estimating the parameters by a repeated measurement model. In addition, ignoring the overdispersion to which count data is prone leads to an increase of the type one error rate. We carry out simulation studies using several different data settings and compare different multiple contrast tests with parameter estimates from generalized estimation equations and generalized linear mixed models in order to observe coverage and rejection probabilities. We generate overdispersed, clustered count data in small samples as can be observed in many biological settings. We have found that the generalized estimation equations outperform generalized linear mixed models if the variance-sandwich estimator is correctly specified. Furthermore, generalized linear mixed models show problems with the convergence rate under certain data settings, but there are model implementations with lower implications exists. Finally, we use an example of genetic data to demonstrate the application of the multiple contrast test and the problems of ignoring strong overdispersion.     

福费廷服务的法律思考

福费廷是一种新兴的以无追索权为特点的国际融资服务项目。西方国家的绝大多数大银行都开展了此项业务,而我国银行和贸易商对此了解不多。中国在入世时承诺的五年过渡期即将结束,外资银行纷纷抢滩中国市场,凭借其丰富的管理经验和优质多样的服务品种积极争夺中国国内的优质客户,南京爱立信"倒戈"花旗银行便是例证。中国的银行业面临前所未有的严峻局面。福费廷的研究和利用能使中资银行在竞争中获得一席之地,更好地迎接挑战。     

吉林省土地征收中农民权利探析

随着吉林省经济的迅速发展和农村城市化进程的加快,对农村土地的征收越来越多,越来越频繁。土地征收既要最大限度保护农民权利,同时也应适当结合平衡原则加以考虑。但是,由于我国现阶段土地征收制度不健全,侵犯农民权利的现象屡有发生,对吉林省农村的稳定产生了消极影响。通过深入分析吉林省土地征收中农民权利现状,提出完善现行土地征收法律制度的对策。     

冰箱化霜温控开关温度特性全自动测试台

本文介绍了自行研制的冰箱化霜温控开关温度特性全自动测试合，它每次检测数可达１００只，工作槽温度场均匀性在±０．１℃以内，控温精度达±０２℃．文中对其设计原理、系统流程及控制系统等作了详细描述．     

German family policy at the crossroads: analysing the impact of parental leave reform through simulation

Comparative studies of welfare reforms encounter two problems. First, the counterfactual problem is that in the real world schemes and their reforms do not coexist simultaneously and are hard to compare. Second, the contextual problem derives from the absence of comparable measures for change. Microsimulation helps to overcome these problems. It compares policy options – actual reforms or reform plans – simultaneously and provides a comparable measure: the disposable income of model families. This article uses a type–case approach to investigate recent reforms of the German parental leave benefit. Simulation makes those reforms comparable over time and across countries. Results show that the profile of the German scheme is changing from 'general family' towards 'dual-earner' support. Furthermore, the recent reforms make the German scheme converge towards the Swedish leave scheme. The recent reforms introduce a new concept of fairness and a focus on gender equality to German family policies.     

地方高校支援农村人力资源开发的思路与对策

建设社会主义新农村是当前和今后一个时期我国各级政府和有关部门的重大任务,作为政府投资的高等办学机构,地方高等学校有着义不容辞的责任和义务。高校应充分发挥其人才、技术和设施的优势,采取多种形式参与农村人力资源开发,促进新农村建设。