Maximum Likelihood Estimation for Cox's Regression Model Under Case–Cohort Sampling

Abstract.  Case–cohort sampling aims at reducing the data sampling and costs of large cohort studies. It is therefore important to estimate the parameters of interest as efficiently as possible. We present a maximum likelihood estimator (MLE) for a case–cohort study based on the proportional hazards assumption. The estimator shows finite sample properties that improve on those by the Self & Prentice [Ann. Statist. 16 (1988)] estimator. The size of the gain by the MLE varies with the level of the disease incidence and the variability of the relative risk over the considered population. The gain tends to be small when the disease incidence is low. The MLE is found by a simple EM algorithm that is easy to implement. Standard errors are estimated by a profile likelihood approach based on EM-aided differentiation.     

中韩日三国未来在经济上的竞争与合作

一、导言(一)改变中的世界经济数千年前,古代中国在比较厚实的基础之上,就已发展出灿烂的文化,而这先进的文化与经济也通过“丝绸之路”向西方传播。     

Differentials in Adult Mortality and Activity Limitation by Years of Education in the United States at the End of the 1990s

This study examines mortality differentials and health disparities between educational groups within the 1998 adult population (ages 25 and older) in the United States. Mortality differentials are measured using average life expectancy and health disparities by expected years without activity limitation. The results indicate that for both sexes, higher education is associated with higher life expectancy. Those with higher levels of education also have higher life expectancy without activity limitation. Adults with higher education can also expect to enjoy a greater percentage of their expected lives free of any form of activity limitation. At each level of education, adult females have a higher level of activity limitation compared to adult males. At the same level of education, adult females expect to enjoy smaller percentages of their remaining lives free of activity limitation compared to adult males of the same age.     

Physical fitness effects on substance abuse risk factors and use patterns

In this study, seventy-four adolescents in either a school, community or hospital based drug intervention program received and eight to nine week structured fitness activity class as an integrated element of their respective prevention or treatment program. Prepost assessments indicated significant gains in the field fitness tests of one mile run, 1 minute situp, 1 minute pushup, percent fat and flexibility for the total sample. Based upon prepost change on the one mile run time (less than 1:00) subjects were categorized as improvers (n = 38) and non-improvers (n = 36). Improvers demonstrated a significant increase in the self concept risk factor (Piers Harris Self Concept Scale) and a significant decrease in anxiety and depression risk factors (General Well-Being Scale) compared to the non-improvers. At posttest, the improvers self reported substance use patterns were significantly lower compared to the non-improvers for percentage of the sample who were multiple drug users and alcohol uses per week and were significantly higher for the percentage of the sample demonstrating total abstinence. These findings are suggestive of the usefulness of physical training as a supplemental intervention for adolescent substance abusers.     

Income, Environmental Disamenity, and Toxic Releases

The literature argues that income growth leads to increased demand for environmental quality and thus reduction in pollution. Using a utility theoretic model, we hypothesize that the income–pollution relationship should depend on the level of disamenity of the pollutant. We proxy for disamenity using the toxicity of releases. For counties in the United States, the functional relationship between income and releases depends on the level of disamenity: the form is more concave for more toxic releases. We find that environmental improvements occur at lower levels of per capita income for more toxic pollutants.     

CONCOMITANT SCALE ESTIMATION IN REGRESSION PROBLEMS WITH INCREASING DIMENSION

We obtain Bahadur representations for the semi-interquartile range and the median deviation when these estimators are based on the residuals from a linear regression model with increasing dimension. These representations yield a variety of central limit theorems and conditions under which the two estimators are equivalent. In particular, the representations justify the use of the estimators as concomitant scale estimators in general scale equivariant M-estimation of a regression parameter when the dimension of the parameter increases with the sample size.     

Working Unusual Hours and Its Relationship to Job Satisfaction: A Study of European Maritime Pilots

Our study focuses on maritime pilotage in seven European countries and analyzes the level of job satisfaction and its predictors. Like most existing studies in the field of job satisfaction, we show that job satisfaction is an outcome of the work of maritime pilots. Stressful working conditions, such as working unsocial hours and irregular working patterns, create strains that together with intervening factors related to work, family, or the work environment ultimately reduce job satisfaction. However, our results indicate that although negative physical and social consequences are important, they are neither the strongest nor the only variables determining job satisfaction. Another effect seems more important in European maritime pilotage: Job satisfaction is instead a predictor of how much pressure and stress pilots can handle. Despite health problems and a reduction in their quality of life due to working unusual hours, most maritime pilots do not regret their choice of profession. Factors to ameliorate the working conditions are also identified. The most important parameters include alterations in working time systems, working conditions which minimize physical strain, fairness regarding payment, flexibility within the compensation system, an intensification of the possibilities for involvement and participation, an extended degree of co-determination, and the distribution of the ownership of the pilot stations.     

经济全球化与中国经济的发展

经济全球化已成为当今世界经济发展的一个不可逆转的大趋势。中国只有正确认识和把握经济全球化的规律 ,抓住机遇 ,趋利避害 ,才能获得发展的主动权