Mixed-effects Models with Skewed Distributions for Time-varying Decay Rate in HIV Dynamics

After initiation of treatment, HIV viral load has multiphasic changes, which indicates that the viral decay rate is a time-varying process. Mixed-effects models with different time-varying decay rate functions have been proposed in literature. However, there are two unresolved critical issues: (i) it is not clear which model is more appropriate for practical use, and (ii) the model random errors are commonly assumed to follow a normal distribution, which may be unrealistic and can obscure important features of within- and among-subject variations. Because asymmetry of HIV viral load data is still noticeable even after transformation, it is important to use a more general distribution family that enables the unrealistic normal assumption to be relaxed. We developed skew-elliptical (SE) Bayesian mixed-effects models by considering the model random errors to have an SE distribution. We compared the performance among five SE models that have different time-varying decay rate functions. For each model, we also contrasted the performance under different model random error assumptions such as normal, Student-t, skew-normal, or skew-t distribution. Two AIDS clinical trial datasets were used to illustrate the proposed models and methods. The results indicate that the model with a time-varying viral decay rate that has two exponential components is preferred. Among the four distribution assumptions, the skew-t and skew-normal models provided better fitting to the data than normal or Student-t model, suggesting that it is important to assume a model with a skewed distribution in order to achieve reasonable results when the data exhibit skewness.     

Comparison of hazard rates for dependent random variables

In this paper, we define and study a new notion for the comparison of the hazard rates of two random variables taking into account their mutual dependence. Properties, applications and the comparison for a data set are given.     

Understanding Estimators of Treatment Effects in Regression Discontinuity Designs

In this paper, we propose two new estimators of treatment effects in regression discontinuity designs. These estimators can aid understanding of the existing estimators such as the local polynomial estimator and the partially linear estimator. The first estimator is the partially polynomial estimator which extends the partially linear estimator by further incorporating derivative differences of the conditional mean of the outcome on the two sides of the discontinuity point. This estimator is related to the local polynomial estimator by a relocalization effect. Unlike the partially linear estimator, this estimator can achieve the optimal rate of convergence even under broader regularity conditions. The second estimator is an instrumental variable estimator in the fuzzy design. This estimator will reduce to the local polynomial estimator if higher order endogeneities are neglected. We study the asymptotic properties of these two estimators and conduct simulation studies to confirm the theoretical analysis.     

中国农村民间借贷市场融资约束环境下利率定价模型分析——以广东农村实地调查数据为例

通过对广东农户民间借贷行为实地调查的问卷进行数据分析,了解农村民间借贷中的资金供求关系,发现存在的融资约束问题,进而对融资约束环境下民间借贷资金利率定价过程进行实证分析;着重考察农村民间借贷利率受公共信息和私人信息影响的程度,从借款人和贷款人的角度分别建立定价模型进行经验分析。结果显示,定价模型在F检验1%水平上显著,其他模型具有R2的统计显著性;反映借款用途的变量在10%水平上显著,其他变量均在5%水平上显著。这说明该市场利率能够反映公共信息的影响,借款人和贷款人的利率定价也反映了各自私人信息中相关风险和财务能力因素的影响,得到的经验结论主要是:第一,农村民间借贷市场是自主交易的金融市场;第二,其利率定价过程基本市场化。     

上市公司债务重组财务效应研究

债务重组是很多企业在生产经营活动中遇到的重大问题,债务重组的结果如何,会对企业产生重大影响。在分析了中国深圳和上海证券交易所的上市公司的债务重组的相关数据之后,得出了债务重组能够显著改善企业业绩的相关结论,提出了要加强对债务重组信息披露等相关建议。     

完善我国个人所得税制的思考

个人所得税是调节国家与个人利益分配关系的重要杠杆,随着我国经济的快速发展、居民收入水平的大幅提高,个人所得税将是一项最有前途、最有发展潜力的税种。但我国个人所得税政策不尽人意,执行起来既失公平,又欠效率。文章分析了我国个人所得税制存在的问题,提出了相应的对策。     

理工农医院校社科学报转引率偏低原因分析

理工农医院校社科学报由于办刊时间短,作者群不稳定,实用性文章较多,发行量少,学术界影响小,以及社会和学术界的偏见,致使转引率偏低。为此,理工农医院校社科学报要加强自身建设,走特色办刊原则,强化编辑队伍,建立稳定的作者群,坚持正确的办刊原则,以尽快提高学报质量。     

网络集群的自组织特征 —— 以“南京梧桐树事件”的微博维权为个案

近年来,伴随着急剧的社会结构转型,我国新的社会身份和社会认同群体也随之产生,在网络中的政治表达和利益维护活动增多,在这些网络讨论的集群内部,参与者会自发形成一定的秩序,推动事件的进行。本研究利用自组织理论作为分析框架,选取"南京梧桐树事件"的微博维权集群为研究对象,重点考察网络集群参与者之间从无序到有序的互动过程、整个系统的演变规律及其与外界的互动机制,由此总结出网络集群中的自组织特征,从而相对准确地把握虚拟社区系统的发展、演化阶段,为更好地理解互联网的社会功能起到借鉴作用,也为政府有关部门做好群体事件的预防工作提供理论和策略上的支持。     

Smoothed bootstrap bandwidth selection for nonparametric hazard rate estimation

A smoothed bootstrap method is presented for the purpose of bandwidth selection in nonparametric hazard rate estimation for iid data. In this context, two new bootstrap bandwidth selectors are established based on the exact expression of the bootstrap version of the mean integrated squared error of some approximations of the kernel hazard rate estimator. This is very useful since Monte Carlo approximation is no longer needed for the implementation of the two bootstrap selectors. A simulation study is carried out in order to show the empirical performance of the new bootstrap bandwidths and to compare them with other existing selectors. The methods are illustrated by applying them to a diabetes data set.