Proportional hazards model for discrete data: Some new developments

ABSTRACT

Many times, a product lifetime can be described through a non negative integer valued random variable. In this article, we propose a proportional hazards model for discrete data analogous to the version for continuous data. Some ageing properties of the model are discussed. Stochastic comparison of pair of random variables that follow the model are also made. A new test based on U-statistics is developed for testing that the proportionality parameter in the proposed model is 1. The asymptotic properties of the proposed test are studied. We present some numerical results to asses the performance of the test procedure.     

On mantel-haenszel type estimators in simple nested case-control studies

We are concerned with nested case-control studies in this article. For proportional hazards model, a class of over-all estimators of hazard ratios is presented when simple samples are drawn from risk sets. These estimators have the form of the Mantel-Haenszel estimator of odds ratio, and are consistent not only for large strata, but also for sparse data. Consistent estimators of the variances of the proposed hazard ratio estimators are also developed. An example is given to illustrate the proposed estimators.     

A Survey of Microcomputer Survival Analysis Software: The Need for an Integrated Framework

This paper surveys commercially available MS-DOS and Microsoft Windows based microcomputer software for survival analysis, especially for Cox proportional hazards regression and parametric survival models. Emphasis is given to functionality, documentation, generality, and flexibility of software. A discussion of the need for software integration is given, which leads to the conclusion that survival analysis software not closely tied to a well-designed package will not meet an analyst's general needs. Some standalone programs are good tools for teaching the theory of some survival analysis procedures, but they may not teach the student good data analysis techniques such as critically examining regression assumptions. We contrast typical software with a general, integrated, modeling framework that is available with S-PLUS.     

Dynamic Simulation as an Approach to Understanding Hurricane Risk Response: Insights from the Stormview Lab

This article investigates the use of dynamic laboratory simulations as a tool for studying decisions to prepare for hurricane threats. A prototype web‐based simulation named Stormview is described that allows individuals to experience the approach of a hurricane in a computer‐based environment. In Stormview participants can gather storm information through various media, hear the opinions of neighbors, and indicate intentions to take protective action. We illustrate how the ability to exert experimental control over the information viewed by participants can be used to provide insights into decision making that would be difficult to gain from field studies, such as how preparedness decisions are affected by the nature of news coverage of prior storms, how a storm's movement is depicted in graphics, and the content of word‐of‐mouth communications. Data from an initial application involving a sample of Florida residents reveal a number of unexpected findings about hurricane risk response. Participants who viewed forecast graphics, which contained track lines depicting the most likely path of the storm, for example, had higher levels of preparation than those who saw graphics that showed only uncertainty cones—even among those living far from the predicted center path. Similarly, the participants who were most likely to express worry about an approaching storm and fastest to undertake preparatory action were those who, ironically, had never experienced one. Finally, external validity is evidenced by a close rank‐order correspondence between patterns of information use revealed in the lab and that found in previous cross‐sectional field studies.     

The gendered dimensions of bushfire in changing rural landscapes in Australia

This paper examines gender differences in awareness, preparedness and attitudes towards bushfire amongst landholders in rural landscapes affected by amenity-led in-migration in southeast Australia. It considers the potential of conceptualising bushfire not as a gender-neutral natural phenomenon but as an important means by which traditional gender roles and power relations within rural landscapes are maintained. Landholders were found to uphold conventional views of bushfire management as “men’s business” despite changing social circumstances. Consequently, key gender differences exist within landholders’ bushfire risk awareness, bushfire knowledge, the perceived need for bushfire preparedness measures, the willingness to perform certain tasks, and the belief in personal capacity to act. We argue that covert and less visible as well as overt gender roles and traditions are important factors in understanding landholders’ engagement with bushfire management. When gendered dimensions of bushfire are investigated in the context of hegemony, a paradox emerges between women choosing not to take control of their own bushfire safety and women being denied the opportunity to take control. The complex and contradictory actions and attitudes to bushfire that materialise through an analysis of gendered social experiences complicate attempts to create more gender-sensitive frameworks for bushfire management. The tenacious and embedded nature of gender role divisions within both public and private spheres was furthermore found to act as economic, social and political stumbling blocks for empowerment opportunities. Using a mixed-methods research approach, this paper maps out gendered dimensions of bushfire through landholders’ narratives and actions. The implications of these dimensions for bushfire management have direct relevance to recent international discussions of the vulnerability of the growing number of people living in bushfire-prone rural–urban interface areas.     

历史虚无主义思潮对大学生思想政治教育影响研究

历史虚无主义思潮通过否定和歪曲中国近现代史、贬损历史人物形象,进而否定中国特色社会主义的道路、理论和制度,致使部分大学生失掉了中国特色社会主义的道路自信、理论自信和制度自信,给大学生思想政治教育工作带来严峻挑战。高校思想政治教育工作者应认清历史虚无主义思潮的主要表现与危害,分析其在大学生群体中传播的原因,进而通过改革思想政治理论课教学、加强大学生社会实践、占领微传播渠道传播正确的历史知识等措施,消除历史虚无主义思潮对大学生思想政治教育的影响。     

A class of tests of proportional hazards assumption for left-truncated and right-censored data

In this paper, we proposed a class of tests of proportional hazards assumption for left-truncated and right-censored data based on a pair of estimators of the hazard ratio constant. Using counting process and martingale theory, the asymptotically normal distribution of the test statistic is derived and a family of consistent estimators of variance are also provided. Extensive simulation studies were conducted to evaluate the performance of the proposed test statistics under finite sample situations. Two real data sets are analyzed to illustrate our method.     

Estimation of the mean quality-adjusted survival using a multistate model for the sojourn times

In clinical trials, it may be of interest taking into account physical and emotional well-being in addition to survival when comparing treatments. Quality-adjusted survival time has the advantage of incorporating information about both survival time and quality-of-life. In this paper, we discuss the estimation of the expected value of the quality-adjusted survival, based on multistate models for the sojourn times in health states. Semiparametric and parametric (with exponential distribution) approaches are considered. A simulation study is presented to evaluate the performance of the proposed estimator and the jackknife resampling method is used to compute bias and variance of the estimator.     

A family of distributions to model load sharing systems

The main characteristic of a load sharing system is that after the failure of one component the surviving components have to shoulder extra load and hence are prone to failure at an earlier time than what is expected under the original model. In others, the failure of one component may release extra resources to the survivors, thus delaying the system failure. In this paper we consider such m component systems and some observation schemes and identifiability issues under them. Then we construct a general semiparametric multivariate family of distributions which explicitly models this phenomenon through proportional conditional hazards. We suggest estimates for the constant of proportionality. We propose a nonparametric test for the hypothesis that the failures take place independently according to the common distribution against the alternative hypothesis that the second failure takes place earlier than warranted, study its properties and illustrate its use.     

A Study of Suicide Risk Using a Cox Cure Model via a Retrospective Sampling and Multiple Imputation

The incidence of suicide is an example of rare event. A Cox cure model is adopted to examine the suicide risk of a cohort study of a sample of 65,000 Personal Emergency Link users over a 10-year observation period. Our objective is to investigate the effect of personal covariates on the failure time to suicide as well as the long-term survival from suicide. Based on the Cox cure model, a new and efficient estimation approach using retrospective sampling and multiple imputation was used. Compared with the standard Cox proportional hazards model, the Cox cure model provides a new perspective on analyzing the suicide data.