Likelihood ratio tests for multivariate normality

This paper presents some powerful omnibus tests for multivariate normality based on the likelihood ratio and the characterizations of the multivariate normal distribution. The power of the proposed tests is studied against various alternatives via Monte Carlo simulations. Simulation studies show our tests compare well with other powerful tests including multivariate versions of the Shapiro–Wilk test and the Anderson–Darling test.     

Reliability analysis of load-sharing systems with memory

The load-sharing model has been studied since the early 1940s to account for the stochastic dependence of components in a parallel system. It assumes that, as components fail one by one, the total workload applied to the system is shared by the remaining components and thus affects their performance. Such dependent systems have been studied in many engineering applications which include but are not limited to fiber composites, manufacturing, power plants, workload analysis of computing, software and hardware reliability, etc. Many statistical models have been proposed to analyze the impact of each redistribution of the workload; i.e., the changes on the hazard rate of each remaining component. However, they do not consider how long a surviving component has worked for prior to the redistribution. We name such load-sharing models as memoryless. To remedy this potential limitation, we propose a general framework for load-sharing models that account for the work history. Through simulation studies, we show that an inappropriate use of the memoryless assumption could lead to inaccurate inference on the impact of redistribution. Further, a real-data example of plasma display devices is analyzed to illustrate our methods.

     

The Representation of Hypergeometric Random Variables using Independent Bernoulli Random Variables

In this paper, we show that a hypergeometric random variable can be represented as a sum of independent Bernoulli random variables that are, except in degenerate cases, not identically distributed. In the proof, we use the factorial moment generating function. An asymptotic result on the probabilities of the Bernoulli random variables in the sum is also presented. Numerical examples are used to illustrate the results.     

On nonparametric variogram estimation

A critical step for geostatistical prediction is estimation of variogram from the data. One of the popular methods estimating variogram is a smoothed version of classical nonparametric variogram estimator. In this paper we investigate its theoretical and empirical properties to provide useful information for using it. The main results are based on asymptotic theories (i.e., risk and central limit theorem) under nearly infill domain sampling. Simulation is also employed to make our points.     

Testing lack of symmetry in spatial–temporal processes

Symmetry and separability of a covariance function are common assumptions to simplify the modeling effort of spatial–temporal processes. However, many studies in environmental sciences show that real data have complex spatial–temporal dependency structures resulting from lack of symmetry or violation of other standard assumptions of the covariance function. In this study, we propose new formal tests for lack of symmetry by using spectral representations of the spatial–temporal covariance functions of regularly spaced spatial–temporal data. The advantage of the proposed tests is that classical analysis of variance (ANOVA) models can be used for detecting lack of symmetry inherent in spatial–temporal processes. We evaluate the performance of the tests with simulation studies and we apply them to air pollution data.     

Mobile use,personal values,and connectedness with civic life

This study aims to examine whether and how mobile communication enables citizens to translate their value orientations into their connectedness to the civic life. Specifically, we probe the indirect process in which different types of personal values predict key dimensions of engagement with civic affairs through patterns of mobile phone use. We show that individualism is indirectly associated with engagement with civic affairs through informational mobile use, whereas the link between collectivism and community involvement is positively intervened by relational mobile use. Additionally, socio-tropic empathy yields indirect relationships with civic engagement through informational mobile use. Implications of these findings are discussed.     

Inside the blogosphere: A taxonomy and framing analysis of abortion weblogs

This study analyses weblog abortion-related content sampled via a search and snowball method. When weblogs located inside of established media Web sites and other weblogs are compared, they are equivalent in the use of advocacy versus objectivist frames. Media weblog posts contain a political frame more frequently than non-media weblog posts do. In terms of diversity of frame, media weblogs employ more frames in their stories. Various explanations for these findings are offered in the context of current abortion-related content patterns.     

Maternal Experiences of Parenting Girls who are Perceived as Overweight or at Risk for Becoming So: Narratives of Uncertainty,Ambivalence and Struggle

This work explored U.S. mothers’ experiences of parenting young adolescent girls who are perceived by their mothers as overweight or at risk for becoming so. Data were collected via in‐depth interviews with 13 mothers and were analysed using a constructivist grounded theory approach. Many mothers experienced socializing their daughters about issues of the body, weight, diet, and health as marked by uncertainty, ambivalence and struggle, particularly relative to four subthemes: mothers’ embodiment as challenge to ‘good mothering’, negotiating a dilemma of the ‘healthy mind’ versus the ‘healthy body’, managing discipline: how much to intervene?, and the challenge of interpersonal dynamics.