Failure Inference From a Marker Process Based on a Bivariate Wiener Model

Many models have been proposed that relate failure times and stochastic time-varying covariates. In some of these models, failure occurs when a particular observable marker crosses a threshold level. We are interested in the more difficult, and often more realistic, situation where failure is not related deterministically to an observable marker. In this case, joint models for marker evolution and failure tend to lead to complicated calculations for characteristics such as the marginal distribution of failure time or the joint distribution of failure time and marker value at failure. This paper presents a model based on a bivariate Wiener process in which one component represents the marker and the second, which is latent (unobservable), determines the failure time. In particular, failure occurs when the latent component crosses a threshold level. The model yields reasonably simple expressions for the characteristics mentioned above and is easy to fit to commonly occurring data that involve the marker value at the censoring time for surviving cases and the marker value and failure time for failing cases. Parametric and predictive inference are discussed, as well as model checking. An extension of the model permits the construction of a composite marker from several candidate markers that may be available. The methodology is demonstrated by a simulated example and a case application.     

回归模型中异性方差问题的克服

提出了回归分析中异性方差的检验和对估计结果带来的影响以及消除其异方差性的两种方法：对原模型进行变换和加权最小二乘法．     

Modelling Variability in the Branching Structure of Strawberry Inflorescences

The branching structure of inflorescences of the cultivated strawberry ( Fragaria × ananassa Duch.) is very variable. This paper demonstrates that some aspects of this variability are well described by a simple stochastic model of branching that has two adjustable parameters. The model is shown to provide a good fit to data from a set of almost 700 inflorescences of the cultivar Elsanta, collected over two successive years. For one parameter the maximum likelihood estimator is a moment estimator which is fully efficient even if the detailed branching structure of the inflorescences is not recorded. This parameter provides a convenient summary of branching vigour. The maximum likelihood estimator of the second parameter must be determined iteratively and can be quite inefficient unless the full branching structure is recorded. The model demonstrates that branching structure is affected by the order in which inflorescences emerge on the plant.     

Extensions of Fill's algorithm for perfect simulation

Fill's algorithm for perfect simulation for attractive finite state space models, unbiased for user impatience, is presented in terms of stochastic recursive sequences and extended in two ways. Repulsive discrete Markov random fields with two coding sets like the auto-Poisson distribution on a lattice with 4-neighbourhood can be treated as monotone systems if a particular partial ordering and quasi-maximal and quasi-minimal states are used. Fill's algorithm then applies directly. Combining Fill's rejection sampling with sandwiching leads to a version of the algorithm which works for general discrete conditionally specified repulsive models. Extensions to other types of models are briefly discussed.     

Expressing Estimators of Expected Quality Adjusted Survival as Functions of Nelson-Aalen Estimators

Quality adjusted survival has been increasingly advocated in clinical trials to be assessed as a synthesis of survival and quality of life. We investigate nonparametric estimation of its expectation for a general multistate process with incomplete follow-up data. Upon establishing a representation of expected quality adjusted survival through marginal distributions of a set of defined events, we propose two estimators for expected quality adjusted survival. Expressed as functions of Nelson-Aalen estimators, the two estimators are strongly consistent and asymptotically normal. We derive their asymptotic variances and propose sample-based variance estimates, along with evaluation of asymptotic relative efficiency. Monte Carlo studies show that these estimation procedures perform well for practical sample sizes. We illustrate the methods using data from a national, multicenter AIDS clinical trial.     

国际视野的我国电视产品内容规制

内容提要在电视传媒产业化进程中,出于电视节目事关意识形态和国家文化安全,政府有必要对电视节目内容进行规制。电视产品的外部性和信息不对称引致的市场失灵是政府对电视产品内容实行规制的动因。国内外电视产品内容规制的实践证明,从内容质量和限制境外电视节目播出方面进行规制对保护电视传媒业是完全有必要的。对电视节目的内容规制,我国现实且明智的政策只能是在开放中实施保护,在保护中实施开放。     

The Time Series and Cross‐Section Asymptotics of Dynamic Panel Data Estimators

In this paper we derive the asymptotic properties of within groups (WG), GMM, and LIML estimators for an autoregressive model with random effects when both T and N tend to infinity. GMM and LIML are consistent and asymptotically equivalent to the WG estimator. When T/N→ 0 the fixed T results for GMM and LIML remain valid, but WG, although consistent, has an asymptotic bias in its asymptotic distribution. When T/N tends to a positive constant, the WG, GMM, and LIML estimators exhibit negative asymptotic biases of order 1/T, 1/N, and 1/(2N−T), respectively. In addition, the crude GMM estimator that neglects the autocorrelation in first differenced errors is inconsistent as T/N→c>0, despite being consistent for fixed T. Finally, we discuss the properties of a random effects pseudo MLE with unrestricted initial conditions when both T and N tend to infinity.     

A case study of failure to thrive and inter‐agency work

Social workers and medical professionals have an ambiguous relationship. Though expected to work together within the child protection regulations of the Children Act 1989, there are many tensions. In general, social workers and health visitors enjoy close working relationships, but tensions are frequently experienced as one proceeds higher up the medical hierarchy. The reasons for this may be numerous, but in practice may obstruct speedy action in detection and prevention of disease which is social in aetiology — yet all professionals have an important role. I hope to demonstrate this in the following case study, where ‘failure to thrive’ took 18 months to evidence but, without inter‐agency working, might have proved fatal to the child. Copyright © 2000 John Wiley & Sons, Ltd.     

不公平有几何？——中国城市居民收入分配公平感的测量

文章首先通过批判性地介绍几种已有的公平感测量方法,选取其中最为合适的一种在CGSS2005数据基础上测量中国城市居民的反身性公平感和非反身性公平感。其次,分别以性别、年龄、教育和单位体制变量分组,从多方面呈现了两种公平感在中国的现状。最后,作者通过使用对总体样本进行随机性拆分得到的两个样本对此测量方法的信度进行了验证。     

企业局域网常见故障及解决办法

在当今社会,越来越多的企业将网络技术运用到实际生产工作当中.网络技术在给企业带来便利的同时,也耗费了企业大量的人力、物力、财力进行维护.文章从五方面探讨了企业局域网常见故障及解决办法.