Stratified proportional subdistribution hazards model with covariate-adjusted censoring weight for case-cohort studies

The case-cohort study design is widely used to reduce cost when collecting expensive covariates in large cohort studies with survival or competing risks outcomes. A case-cohort study dataset consists of two parts: (a) a random sample and (b) all cases or failures from a specific cause of interest. Clinicians often assess covariate effects on competing risks outcomes. The proportional subdistribution hazards model directly evaluates the effect of a covariate on the cumulative incidence function under the non-covariate-dependent censoring assumption for the full cohort study. However, the non-covariate-dependent censoring assumption is often violated in many biomedical studies. In this article, we propose a proportional subdistribution hazards model for case-cohort studies with stratified data with covariate-adjusted censoring weight. We further propose an efficient estimator when extra information from the other causes is available under case-cohort studies. The proposed estimators are shown to be consistent and asymptotically normal. Simulation studies show (a) the proposed estimator is unbiased when the censoring distribution depends on covariates and (b) the proposed efficient estimator gains estimation efficiency when using extra information from the other causes. We analyze a bone marrow transplant dataset and a coronary heart disease dataset using the proposed method.     

唤醒心中的天使

解放军战士雷锋是伟大的楷模。雷锋省吃俭用,生活朴素,穿着打补丁的袜子,人家喝汽水的时候他喝白开水,一分一分积攒下来的钱默默无闻地捐给灾区。在去医院看病的路上看到工地缺少搬砖人手,他竟忘却了自己带病的身体还和别人展开了搬砖比赛。吃苦在前、一生都为别人服务的他仅仅20多岁就离开了人世,但他的事迹传遍了整个中国,毛泽东主席还题辞"向雷锋同志学习",全中国掀起了学习雷锋的热潮。雷锋唤醒了我心中的天使!无论是中国人还是韩国人,全世界人类心中都有"天使",重要的是你是     

Estimation of long-run inefficiency levels: a dynamic frontier approach

Cornwell, Schmidt, and Sickles (1990) and Kumbhakar (1990), among others, developed stochasticfrontier production models which allow firm specific inefficiency levels to change over time. These studies assumed arbitrary restrictions on the short-run dynamics of efficiency levels which have little theoretical justification. Further, the models are inappropriate for estimation of long-run efficiencies. We consider estimation of an alternative frontier model in which firmspecific technical inefficiency levels are autoregressive. This model is particularly useful to examine a potential dynamic link between technical innovations and production inefficiency levels. We apply our methodology to a panel of US airlines.     

Emancipation under the great recession in Spain

In this paper we document the behavior of emancipation over one of the biggest boom–bust cycles experienced by the Spanish economy. In principle, the economic difficulties faced by the Spanish youth during the last recession would have hampered a normal emancipation pace. However, we find that the proportion living away from parents among those aged 18–40 has not decreased but increased from 44 % during the boom (2005–2008) to 46 % during the bust (2009–2013). A simple decomposition reveals that this is mainly driven by the substantial rise in the emancipation rate among the full-time employed workers during the bust. To explain this change we discuss several factors such as macroeconomic conditions, rental subsidy policy, higher labor mobility, selection bias, reverse causation, time-lag in adjustment and secular trend.     

Korean students’ minority schooling experience in Japan

A qualitative study conducted in western Japan examined the perceptions of Korean students in Japanese junior high school to identify factors contributing to a consistently low high school advancement rate compared to mainstream Japanese students. Fourteen people were interviewed about their Korean students’ experiences in Japan. The findings of this study suggest that factors contributing to the low high school advancement rate among Korean students cluster around three themes: (1) discrimination experienced in society at large and at school, (2) assimilation to become more like the Japanese, and (3) inconsistent cultural and insufficient academic support given by the school and teachers. Findings from this study indicate how the power structure in a social context of schooling influences minority students’ learning and also confirmed in part Ogbu and Cummins’ theories of how power relations between the subordinated and the dominant affect minority students’ schooling experiences and learning.     

Effects of 360° video on attitudes toward disaster communication: Mediating and moderating roles of spatial presence and prior disaster media involvement

Visual media technologies such as 360° video, augmented reality, and virtual reality are on the rise for immersive storytelling in a variety of public relations contexts. Yet there is a profound lack of scholarly research in public relations, crisis communication, and disaster communication to explore the effects of content displayed using these delivery formats on publics’ responses. To begin addressing the knowledge gap, this work reports results from a laboratory experiment investigating effects of media modality (traditional unidirectional video content vs. 360° omnidirectional video content) on attitudes toward the disaster communication content. Results demonstrate that 360° video featuring the aftermath of a natural disaster yields enhanced attitudes toward the helpful impact of the content. Importantly, mediation analyses show that (1) a sense of spatial presence underlies these effects, and (2) the mediating effects of spatial presence are attenuated by involvement with similar disaster media coverage (indirect experience).     

Investigating dependence between frequency and severity via simple generalized linear models

Recently, a body of literature proposed new models relaxing a widely-used but controversial assumption of independence between claim frequency and severity in non-life insurance rate making. This paper critically reviews a generalized linear model approach, where a dependence between claim frequency and severity is introduced by treating frequency as a covariate in a regression model for severity. As an extension of this approach, we propose a dispersion model for severity. For this model, the information loss caused by using average severity rather than individual severity is examined in detail and the parameter estimators suffering from low efficiency are identified. We also provide analytical solutions for the aggregate sum to help rate making. We show that the simple functional form used in current research may not properly reflect the real underlying dependence structure. A real data analysis is given to explain our analytical findings.     

Grandparent caregiving and cognitive functioning among older people: evidence from Korea

Review of Economics of the Household - Caregiving for grandchildren is becoming common and plays an important role in the childcare system in many countries. This study examines whether caregiving...     

Empirical Likelihood‐Based Inference in Conditional Moment Restriction Models

This paper proposes an asymptotically efficient method for estimating models with conditional moment restrictions. Our estimator generalizes the maximum empirical likelihood estimator (MELE) of Qin and Lawless (1994). Using a kernel smoothing method, we efficiently incorporate the information implied by the conditional moment restrictions into our empirical likelihood‐based procedure. This yields a one‐step estimator which avoids estimating optimal instruments. Our likelihood ratio‐type statistic for parametric restrictions does not require the estimation of variance, and achieves asymptotic pivotalness implicitly. The estimation and testing procedures we propose are normalization invariant. Simulation results suggest that our new estimator works remarkably well in finite samples.