Reducing sample size needed for cox-proportional hazards model analysis using more efficient sampling method

Abstract

In general, survival data are time-to-event data, such as time to death, time to appearance of a tumor, or time to recurrence of a disease. Models for survival data have frequently been based on the proportional hazards model, proposed by Cox. The Cox model has intensive application in the field of social, medical, behavioral and public health sciences. In this paper we propose a more efficient sampling method of recruiting subjects for survival analysis. We propose using a Moving Extreme Ranked Set Sampling (MERSS) scheme with ranking based on an easy-to-evaluate baseline auxiliary variable known to be associated with survival time. This paper demonstrates that this approach provides a more powerful testing procedure as well as a more efficient estimate of hazard ratio than that based on simple random sampling (SRS). Theoretical derivation and simulation studies are provided. The Iowa 65+ Rural study data are used to illustrate the methods developed in this paper.     

A class of additive transformation models for recurrent gap times

Abstract

The gap time between recurrent events is often of primary interest in many fields such as medical studies, and in this article, we discuss regression analysis of the gap times arising from a general class of additive transformation models. For the problem, we propose two estimation procedures, the modified within-cluster resampling (MWCR) method and the weighted risk-set (WRS) method, and the proposed estimators are shown to be consistent and asymptotically follow the normal distribution. In particular, the estimators have closed forms and can be easily determined, and the methods have the advantage of leaving the correlation among gap times arbitrary. A simulation study is conducted for assessing the finite sample performance of the presented methods and suggests that they work well in practical situations. Also the methods are applied to a set of real data from a chronic granulomatous disease (CGD) clinical trial.     

Price bias and common practice in option pricing

Generally, the semiclosed-form option pricing formula for complex financial models depends on unobservable factors such as stochastic volatility and jump intensity. A popular practice is to use an estimate of these latent factors to compute the option price. However, in many situations this plug-and-play approximation does not yield the appropriate price. This article examines this bias and quantifies its impacts. We decompose the bias into terms that are related to the bias on the unobservable factors and to the precision of their point estimators. The approximated price is found to be highly biased when only the history of the stock price is used to recover the latent states. This bias is corrected when option prices are added to the sample used to recover the states' best estimate. We also show numerically that such a bias is propagated on calibrated parameters, leading to erroneous values. The Canadian Journal of Statistics 48: 8–35; 2020 © 2019 Statistical Society of Canada     

Mediation Role of Dyadic Coping on Parenting Stress and Relational Resilience in Couples

This study aims to explore the mediating role of dyadic coping between relational resilience and parenting stress on married couples. The study participants comprised 229 married couples with at least one child and who have had a major life event. The relational resilience scale, parenting stress inventory, dyadic coping scale and personal information, and life events forms were used to collect data for this study. Data were analyzed with the actor–partner interdependence mediation model. The results revealed that dyadic coping actor–partner effects did not mediate between relational resilience and parenting stress. The results were discussed in relation to the social-ecological model and relevant literature. Based on the current findings, recommendations and implications for further research and practice were also proposed.     

Applying a Treatment Effects Model to Investigate Public Amenity Effect on Physical Activity of the Elderly

The increasing elderly population puts significant health, economic, and social burdens on society. Physical activity is one of the most cost-effective ways to maintain the health of the elderly. This study adopts a treatment effects model to investigate the causal relationship between environment attributes and physical activity among the elderly, while taking endogeneity into account. The data were collected from 274 participants by face-to-face interviews in Taichung, Taiwan. Performing physical activity regularly in parks is the most important measure of the amount of physical activity by the elderly. Providing sufficient and accessible parks in metropolitan residential neighborhoods could be one of the most cost-effective ways to promote physical activity for the elderly living in midsize Asian cities.     

Water cycle algorithm for solving the reliability-redundancy allocation problem with a choice of redundancy strategies

Abstract

This paper proposes a new mathematical model for the reliability-redundancy allocation problem (RRAP) with a choice of redundancy strategies. To maximize the reliability of a system, this model chooses the best redundancy strategy from among both active and standby ones for each subsystem. For those with a standby strategy, a continuous time Markov chain model is used to calculate the exact reliability values. In order to solve the proposed mixed-integer non-linear programing model, a powerful evolutionary algorithm, called water cycle algorithm (WCA), is developed and implemented on three famous benchmark problems. Finally, the results of different benchmark problems are compared with those previously reported to show the superiority of the proposed model and the efficiency of WCA.     

障碍研究论述与社会参与：无障碍、通用设计、能力与差异

障碍研究在过去40年的发展奠定了其对公共政策影响的基础。障碍者社会参与的责任逐渐由以往个人承担与调适，转向社会与国家承担。本文简述西方国家障碍研究的两个主要论述--社会模式与普同主义取向，对比这两个主要论述所衍生出的政策：由早期的无障碍设施到通用设计，至最近的能力取向。障碍者参与社会生活与活动是其基本权利的一部分，这项权利内涵具有积极性，需要政府与社会投入资源，改善外部社会结构与环境，使环境对障碍者更为友善，为其社会参与权利提供保障。     

政府减排目标、产业结构与污染减排

政府是污染减排的重要主体,了解其行为对污染减排的作用对提升污染减排效果及实现中国绿色发展具有重要意义。创造性地将政府减排目标纳入研究框架,构建面板门槛模型,从工业污染排放总量的角度分析政府减排目标、产业结构、经济规模等因素对地方污染减排的影响,并用工业污染物强度进行稳健性检验。结果显示,政府减排目标对污染减排的作用存在阶段性不同:经济发展初级阶段,政府减排目标对污染排放总量的作用方向为正; 经济发展水平较高时,作用方向为负; 两者之间存在适应性调整阶段,作用方向具有不确定性,但总体由正向作用向负向作用转变。产业结构对工业污染排放总量的作用方向因污染物种类而异,经济规模对工业污染排放总量作用方向为正。     

Navigating the ethical maze in disability research: ethical contestations in an African context

Despite changes in how disability is viewed, ethical requirements for disability research have hardly changed. Some ethical clearance procedures, processes and practices still consider persons with disabilities as not able, creating unease among researchers and research participants with disabilities themselves. This paper considers five ethical contestations arising from research in the area of disability in an African context: positionality, vulnerability, signed consent, anonymity, and research committee composition. We argue that ethical requirements in practice are still largely based on a medical model of disability and propose that culturally sensitive social and human rights models should influence disability research ethics.     

The effects of individually varying times of observations on growth parameter estimations in piecewise growth model

When using latent growth modeling (LGM), researchers often restrict the factor loadings, while the multilevel modeling (MLM) treats time as a metric variable. However, when individually varying times of observations are concerned in the longitudinal studies, the use of specified loadings would lead to inaccurate estimation. Based on piecewise growth modeling (PGM), this simulation study showed that (i) individually varying times of observations with larger boundaries got worse estimates and model fits when LGM was used; (ii) estimating the PGM across all the simulation situations was robust within MLM, whereas LGM got identically equal estimation with MLM only in the case of time boundaries of ±1 month or shorter; (iii) larger change of slope in piecewise modeling indicated better estimation.