Baseline age effect on parameter estimates in Cox models

The Cox proportional hazards model is widely used in time-to-event analysis. Two time scales are used in practice: time-on-study and chronological age. The former is the most frequently used time scale in clinical studies and longitudinal observation studies. However, there is no general consensus about which time scale is the best. It has been asserted that if the cumulative baseline hazard is exponential or if the age-at-entry is independent of the covariate, then the two models are equivalent. We show that neither of these conditions leads to equivalency. Variability in the age-at-entry of individuals in the study causes the models to differ significantly. This is shown both analytically and through a simulation study. Additionally, we show that the time-on-study model is more robust to changes in age-at-entry than the chronological age model.     

四阶Laguerre型微分方程的左定空间和左定算子

本文讨论了某四阶Laguerre型微分方程的下有界性，并构造了相关的左定空间和左定算子．     

Estimation of P(X>Y) with Topp–Leone distribution

We consider the estimation problem of the probability P=P(X>Y) for the standard Topp–Leone distribution. After discussing the maximum likelihood and uniformly minimum variance unbiased estimation procedures for the problem on both complete and left censored samples, we perform a Monte Carlo simulation to compare the estimators based on the mean square error criteria. We also consider the interval estimation of P.     

Aalen's linear model for doubly censored data

Double censoring often occurs in registry studies when left censoring is present in addition to right censoring. In this work, we examine estimation of Aalen's nonparametric regression coefficients based on doubly censored data. We propose two estimation techniques. The first type of estimators, including ordinary least squared (OLS) estimator and weighted least squared (WLS) estimators, are obtained using martingale arguments. The second type of estimator, the maximum likelihood estimator (MLE), is obtained via expectation-maximization (EM) algorithms that treat the survival times of left censored observations as missing. Asymptotic properties, including the uniform consistency and weak convergence, are established for the MLE. Simulation results demonstrate that the MLE is more efficient than the OLS and WLS estimators.     

半质环的极大零化左理想

证明了两个定理，即（１）设Ｒ是半质环，则Ｒ含有极小左理想当且仅当Ｒ含有极大零化左理想；（２）设Ｒ是不含非零幂零元的质环，则Ｒ只有平凡的左理想或Ｒ不含极小左理想     

论西部农村留守学校建设问题——以四川省绵阳市为研究样本

伴随改革以来三次"民工潮"的泛起,中国西部较贫困县农村产生了"留守学生"问题.当前,农村留守学生已成为当代中国农村基础教育的突出问题;已成为城乡教育协调发展的严重障碍;已制约着社会主义新农村的建设步伐.本文以绵阳市所辖平武、北川等六县为样本进行分析研究,有创新地提出了加快建设西部农村留守学校等四项对策及解决方案.旨在为解决中国西部农村留守学生问题探索出务实的措施和科学的对策.     

当代西方独立左翼的社会主义观述评

西方独立左翼及其社会主义观是在社会主义和资本主义两种制度的变化和斗争中兴起和发展的,也是对国际形势变化的回应与反思的结果。西方独立左翼的社会主义观包含着对社会主义本质和价值观的分析、对社会主义民主的重新认识、对未来社会主义经济制度的设想、对未来社会主义主体的界定以及对未来社会特征的预见。尽管见解不一,却为科学社会主义理论和实践提供了有价值的探索和借鉴。     

奶牛真胃变位手术疗法的实践与研讨

经多年 30余例的临床诊疗实践证明 ,奶牛真胃变位最有效的疗法是一旦确诊 ,尽早采取手术疗法。详述了奶牛真胃变位的诊断 ,手术治疗步骤 ,并就手术中应注意的问题 ,真胃变位的发病机理与预防进行了探讨     

邓小平理论体系的结构创新问题

党的"十四大"提出了邓小平建设有中国特色社会主义理论体系的结构问题,也就是九大板块.邓小平理论体系的结构应该增加三个大问题,即反对和防止"左"的错误理论;廉能政府理论;现代化建设理论.如果把这些问题纳入到邓小平理论中来,就更显得系统性强、理论性强、符合实际.