Use of log−log survival function in modeling time-covariate interactions in Cox regression

Plotting of log−log survival functions against time for different categories or combinations of categories of covariates is perhaps the easiest and most commonly used graphical tool for checking proportional hazards (PH) assumption. One problem in the utilization of the technique is that the covariates need to be categorical or made categorical through appropriate grouping of the continuous covariates. Subjectivity in the decision making on the basis of eye-judgment of the plots and frequent inconclusiveness arising in situations where the number of categories and/or covariates gets larger are among other limitations of this technique. This paper proposes a non-graphical (numerical) test of the PH assumption that makes use of log−log survival function. The test enables checking proportionality for categorical as well as continuous covariates and overcomes the other limitations of the graphical method. Observed power and size of the test are compared to some other tests of its kind through simulation experiments. Simulations demonstrate that the proposed test is more powerful than some of the most sensitive tests in the literature in a wide range of survival situations. An example of the test is given using the widely used gastric cancer data.     

A new alternative to the standard F test for clustered data

The data collection process and the inherent population structure are the main causes for clustered data. The observations in a given cluster are correlated, and the magnitude of such correlation is often measured by the intra-cluster correlation coefficient. The intra-cluster correlation can lead to an inflated size of the standard F test in a linear model. In this paper, we propose a solution to this problem. Unlike previous adjustments, our method does not require estimation of the intra-class correlation, which is problematic especially when the number of clusters is small. Our simulation results show that the new method outperforms the existing methods.     

Confidence interval estimation of the difference between paired AUCs based on combined biomarkers

In many diagnostic studies, multiple diagnostic tests are performed on each subject or multiple disease markers are available. Commonly, the information should be combined to improve the diagnostic accuracy. We consider the problem of comparing the discriminatory abilities between two groups of biomarkers. Specifically, this article focuses on confidence interval estimation of the difference between paired AUCs based on optimally combined markers under the assumption of multivariate normality. Simulation studies demonstrate that the proposed generalized variable approach provides confidence intervals with satisfying coverage probabilities at finite sample sizes. The proposed method can also easily provide P-values for hypothesis testing. Application to analysis of a subset of data from a study on coronary heart disease illustrates the utility of the method in practice.     

Modified inference about the mean of the exponential distribution using moving extreme ranked set sampling

The maximum likelihood estimator (MLE) and the likelihood ratio test (LRT) will be considered for making inference about the scale parameter of the exponential distribution in case of moving extreme ranked set sampling (MERSS). The MLE and LRT can not be written in closed form. Therefore, a modification of the MLE using the technique suggested by Maharota and Nanda (Biometrika 61:601–606, 1974) will be considered and this modified estimator will be used to modify the LRT to get a test in closed form for testing a simple hypothesis against one sided alternatives. The same idea will be used to modify the most powerful test (MPT) for testing a simple hypothesis versus a simple hypothesis to get a test in closed form for testing a simple hypothesis against one sided alternatives. Then it appears that the modified estimator is a good competitor of the MLE and the modified tests are good competitors of the LRT using MERSS and simple random sampling (SRS).     

宁夏人口与生态环境面临的问题及对策

宁夏是少数民族地区,较为宽松的生育政策。导致人口快速增殖。由于宁夏所处的地理位置和历史遗留的生态债务使得境内生态环境十分脆弱。尤其是人口过度增殖已超出了刚性土地资源的有效容纳力。这不仅给环境造成了巨大压力,也进一步加剧了生态环境的恶化。本文通过大量统计数据和实地调研。分析了近年来宁夏人口与生态环境之间存在的亟待解决的矛盾和问题。分析表明,当前宁夏尤其是宁南山区人口数量与人口素质、人口数量与生态存量和生态消费之间表现出了明显的此长彼消的关系。在分析的基础上．提出了人口与生态环境建设方面的政策建议。     

Community-Based Services and Depression from Person-Environment Fit Perspective: Focusing on Functional Impairments and Living Alone

ABSTRACT

Guided by the Person-Environment Fit perspective, we investigated the extent to which personal and environmental factors influence depression among community-dwelling adults. The data came from the special section about community-based service utilization in the 2012 Health and Retirement Study (N=1,710). Although community-based service was not significantly associated with depression after controlling for covariates, respondents with functional limitations and living alone were less likely to be depressed when using community-based services. This study demonstrates the different associations between community-based services and depression depending on personal needs. It discusses the importance of community-based services for aging-in-place policy, particularly among vulnerable populations.     

A transnational networked public sphere of air pollution: analysis of a Twitter network of PM2.5 from the risk society perspective

ABSTRACT

Drawing on digitaltrace data, publicly accessible government documents, and journalistic reports, this research integrates Beck’s risk society theory with digital media theories to examine the mediated process of risk definition and assessment of PM2.5 (particulate matters with a diameter less than 2.5 micrometers) in a networked public sphere. Network and content analysis of a PM2.5 Twitter network shows that political and professional elite remained the most powerful producers of risk definition. Established media played a key role, yet faced challenges from a variety of actors who disseminated and filtered information. Laypersons, while peripheral, actively interacted with elite and established media. The blurring geographic boundary in the PM2.5 Twitter network revealed an emerging transnational public sphere, which, however, was segregated by language. This research advances a layered understanding of the contingent, paradoxical media impact for social changes in a risk society.     

Multi-ethnic school environment from the school leader’s perspective: challenges and approaches to improve multi-cultural competency among teachers in Malaysia

This study aims to identify the challenges and approaches to improve a multicultural competency among teachers in multi-ethnic schools environment based on school leaders’ perspective. Data collection method used in this study is qualitative method. A total of nine school leaders from the states of Kedah, Penang, and Perak were included in the interview session. The results of this study show that the challenges faced by teachers in practicing the multicultural competency are lack of experience toward cultural diversity. A late exposure to cultural diversity makes it difficult for teachers to accept and adapt in a multi-ethnic school environment. The approaches suggested by school leaders to improve the multicultural competency are as follows: (1) Courses on cultural diversity should be organized to enhance the knowledge about cultural diversity; (2) the development of more open and better policy for education system in Malaysia in order to prepare teachers with a higher multicultural competency for teaching students from diverse ethnic and cultural groups; (3) an early exposure to cultural diversity in order to increase the multicultural competency, especially during teaching practicum.