Bivariate Continuous Distributions with Specified Conditional Hazard Functions

Analysis of covariance (ANCOVA) is the standard procedure for comparing several treatments when the response variable depends on one or more covariates. We consider the problem of testing the equality of treatment effects when the variances are not assumed to be equal. It is well known that classical F test is not robust with respect to the assumption of equal variances and may lead to misleading conclusions if the variances are not equal. Ananda (1998 Ananda , M. M. A. ( 1998 ). Bayesian and non-Bayesian solutions to analysis of covariance models under heteroscedasticity . J. Econometrics 86 : 177 – 192 .[Crossref], [Web of Science ®] , [Google Scholar]) developed a generalized F test for testing the equality of treatment effects. However, simulation studies show that the actual size of this test can be much higher than the nominal level when the sample sizes are small, particularly when the number of treatments is large. In this article, we develop a test using the parametric bootstrap approach of Krishnamoorthy et al. (2007 Krishnamoorthy , K. , Lu , F. , Mathew , T. ( 2007 ). A parametric bootstrap approach for ANOVA with unequal variances: Fixed and random models . Computat. Statist. Data Anal. 51 : 5731 – 5742 .[Crossref], [Web of Science ®] , [Google Scholar]). Our simulations show that the actual size of our proposed test is close to the nominal level, irrespective of the number of treatments and sample sizes. Our simulations also indicate that our proposed PB test is more robust, with respect to the assumption of normality, than the generalized F test. Therefore, our proposed PB test provides a satisfactory alternative to the generalized F test.     

An extension of a change-point problem

We consider a specific classification problem in the context of change-point detection. We present generalized classical maximum likelihood tests for homogeneity of the observed sample in a simple form which avoids the complex direct estimation of unknown parameters. This paper proposes a martingale approach to transformation of test statistics. For sequential and retrospective testing problems, we propose the adapted Shiryayev–Roberts statistics in order to obtain simple tests with asymptotic power one. An important application of the developed methods is in the analysis of exposure's measurements subject to limits of detection in occupational medicine.     

Quality management, environmental management and firm performance: A review of empirical studies and issues of integration

Quality management (QM) and environmental management (EM) are two business practices that may affect firm performance. These practices are being increasingly introduced into firms, which often use them jointly owing to their similarities. As a result of these similarities, their integration has become a popular topic of research and practice. In the field of integration, the highest level of integration may be achieved by means of a single, full QM–EM system (QEM) in which QM and EM lose their independence. It is therefore desirable to identify dimensions from which to assess these management practices and their effects on performance. The aim of this paper is to carry out a literature review in order to propose and analyse dimensions for QM, EM, QEM and firm performance, as well as models of cause–effect relationships between these variables. The topics reviewed are the following: (1) the QM and EM dimensions; (2) the empirical studies about QM–performance and EM–performance links; and (3) issues of integration. The review suggests that the large body of QM research may inform EM and QEM. This is so because research on the QM side is more advanced and developed than that on the EM side.     

Nonparametric-likelihood inference based on cost-effectively-sampled-data

Costs associated with the evaluation of biomarkers can restrict the number of relevant biological samples to be measured. This common problem has been dealt with extensively in the epidemiologic and biostatistical literature that proposes to apply different cost-efficient procedures, including pooling and random sampling strategies. The pooling design has been widely addressed as a very efficient sampling method under certain parametric assumptions regarding data distribution. When cost is not a main factor in the evaluation of biomarkers but measurement is subject to a limit of detection, a common instrument limitation on the measurement process, the pooling design can partially overcome this instrumental limitation. In certain situations, the pooling design can provide data that is less informative than a simple random sample; however this is not always the case. Pooled-data-based nonparametric inferences have not been well addressed in the literature. In this article, a distribution-free method based on the empirical likelihood technique is proposed to substitute the traditional parametric-likelihood approach, providing the true coverage, confidence interval estimation and powerful tests based on data obtained after the cost-efficient designs. We also consider several nonparametric tests to compare with the proposed procedure. We examine the proposed methodology via a broad Monte Carlo study and a real data example.     

SPI<Superscript>+</Superscript> Application in Two Countries with the Liberal Welfare Model: Cases of United Kingdom and Chile

For this study, a comprehensive test was conducted on the net effects of age and cohort on political satisfaction in Hong Kong. We use a newly developed methodology of Age–Period–Cohort analysis known as the Cross-Classified Random Effects Model and a pooled dataset of repeated cross-sectional surveys from 1997 to 2014. The findings reveal a U-shaped relationship between age and political satisfaction, in which the level of satisfaction of the youth is between that of the middle-aged and elderly, while the middle-aged express the least satisfaction and the elderly have the highest level of satisfaction. However, cohort effects are relatively weak. There is no evidence that later cohorts are less satisfied than earlier cohorts. These results indicate that the new generation is more politically dissatisfied due to their age rather than their cohort. We also find that period effects interact with age and cohort effects. The recent decline in the political satisfaction of 20-year-olds and of the cohort born in 1986 or later is more pronounced than that of older people and earlier birth cohorts. Under the rule of the current Chief Executive, young people were found to be much more dissatisfied than older people. The rise in the price of housing in recent years has also sharpened the differences in political satisfaction between those of different ages and cohorts.     

Sleepiness,choice consistency,and risk preferences

We investigate the consistency and stability of individual risk preferences by manipulating cognitive resources. Participants are randomly assigned to an experiment session at a preferred time of day relative to their diurnal preference (circadian matched) or at a non-preferred time (circadian mismatched) and choose allocations between two risky assets [using the Choi et al. (Am Econ Rev 27(5):1921–1938, 2007), design]. We find that choices of circadian matched and mismatched subject are statistically similar in terms of satisfying basic requirements for preference consistency. However, mismatched subjects tend to choose riskier asset bundles.     

Microbiological groundwater quality and health indicators in Mexico City

Groundwater quality was evaluated in the southern and western zones of Mexico City, using bacterial indicators and pathogens. Water quality from 40 wells was related to rates of diarrheal disease with 995 individuals interviewed. The focus of this first study on environmental health indicators (EHI) was based on population data (e.g., drinking water supplies and basic sanitation) and displayed using a Geographic Information System (GIS). Sixty percent of the wells monitored comply with the Mexican drinking water standards; however, based on other microbial evidence, 95% of the wells did not provide good quality water for human consumption. No significant differences were detected among hydrogeological zones. When analyzing by microbial indicators, the southern area was shown to be statistically different (p < 0.01) from the western area of the city. The highest rates of diarrheal diseases were detected in the south; the lowest rates were observed in the west. Although wells in the western side of the city appeared to be more contaminated (54%) than in the south (40%), no significant association with health indicators was detected. These preliminary findings suggest ways to improve the potential of EHI, by framing epidemiological data and the use of GIS.