Criterion for the Selection of a Working Correlation Structure in the Generalized Estimating Equation Approach for Longitudinal Balanced Data

The generalized estimating equation is a popular method for analyzing correlated response data. It is important to determine a proper working correlation matrix at the time of applying the generalized estimating equation since an improper selection sometimes results in inefficient parameter estimates. We propose a criterion for the selection of an appropriate working correlation structure. The proposed criterion is based on a statistic to test the hypothesis that the covariance matrix equals a given matrix, and also measures the discrepancy between the covariance matrix estimator and the specified working covariance matrix. We evaluated the performance of the proposed criterion through simulation studies assuming that for each subject, the number of observations remains the same. The results revealed that when the proposed criterion was adopted, the proportion of selecting a true correlation structure was generally higher than that when other competing approaches were adopted. The proposed criterion was applied to longitudinal wheeze data, and it was suggested that the resultant correlation structure was the most accurate.     

Speciation and evolutionary dynamics of asymmetric mating preference

Asymmetric mating preferences occur in two closely related species, if females of one species are highly selective against males of the second, while females of the second show less selection against males of the first species. It has been suggested that such asymmetry is an indicator of common ancestry between the two species, but actual observations are contradictory and inconclusive. We developed a scenario of speciation history and asymmetric mating preference, incorporating invasion dynamicsvia frequency-dependent interspecific sexual competition. A newly isolated (derived) species may form at the periphery of the ancestral species’ distribution by invading a new range. Only a few closely related species would be expected in the new area, while many related species are expected to coexist with the ancestral species. In a peripherally derived species, female mating preferences should be relaxed through sexual character release, owing to a lack of sympatric species and a scarcity of intraspecific mating opportunities. Secondary contacts may then happen as: 1. repeated invasions, i.e. subsequent invasion by the ancestral species into the new range or, 2. backward invasions, i.e. derived species incursions into the ancestral range. Repeated invasions could lead to the coexistence of both the derived species and the newly invading ancestor. Backward invasions by the derived species can succeed only when the derived females develop a strict mating discrimination against the ancestral males. We then expect strong character displacement in the derived species. Thus, peripheral isolation and repeated invasions lead to the relaxed female mating preferences in the derived species and backward invasions lead to stronger female mating preferences in the derived species. This agrees withDrosophila data from Hawaii and the continents. Experimental data of theDrosophila arizonaemojavensis species cluster also support the hypothesis.     

Politeness Strategies in Confrontations of Prejudice

This project draws on the self-regulation of prejudiced responses model and politeness theory to investigate the role of politeness strategies in interpersonal confrontations of prejudice. One hundred and three participants were exposed to experimental confrontations of prejudiced remarks made about Native Americans. The results generally indicate that direct confrontations, which included an explanation of why the response was perceived as prejudiced, were most effective in reducing prejudiced responses and reducing levels of reported prejudice. Furthermore, participants generally accepted confrontations of their prejudiced responses and did not negatively evaluate their confronters. Finally, the more positive politeness participants perceived in the confrontations, the more positively they evaluated their confronter. Implications for theory and the confrontation of prejudice in everyday life are discussed.     

Intercultural competence development via online social networking: the Japanese students’ experience with internationalisation in U.S. higher education

ABSTRACT

This study examines the possibility that interaction through social network platforms can serve as an informal means of developing intercultural competence among international students in higher education settings. Japanese students studying in the United States at a university in the Northwestern US were invited to participate in a mixed-method study involving interviews about their social network use and interactions, and a structured questionnaire measure of intercultural competence development. Overall, the results indicate that those in the top tertile of intercultural competence development tended to describe more proactive social ways and benefits of interacting with potential sources of support over social media, whereas those in the bottom tertile tended to describe the importance and use of social media for passive consumption of information. The implications for the incorporation of social network platforms into higher-education programs for internationalisation and intercultural competence development are discussed.     

Generalized Least Squares Model Averaging

In this article, we propose a method of averaging generalized least squares estimators for linear regression models with heteroskedastic errors. The averaging weights are chosen to minimize Mallows’ C_p-like criterion. We show that the weight vector selected by our method is optimal. It is also shown that this optimality holds even when the variances of the error terms are estimated and the feasible generalized least squares estimators are averaged. The variances can be estimated parametrically or nonparametrically. Monte Carlo simulation results are encouraging. An empirical example illustrates that the proposed method is useful for predicting a measure of firms’ performance.     

Evolution and population dynamics in stochastic environments

Inter-generational temporal variability of the environment is important in the evolution and adaptation of phenotypic traits. We discuss a population-dynamic approach which plays a central role in the analysis of evolutionary processes. The basic principle is that the phenotypes with the greatest long-term average growth rate will dominate the entire population. The calculation of longterm average growth rates for populations under temporal stochasticity can be highly cumbersome. However, for a discrete non-overlapping population, it is identical to the geometric mean of the growth rates (geometric mean fitness), which is usually different from the simple arithmetic mean of growth rates. Evolutionary outcomes based on geometric mean fitness are often very different from the predictions based on the usual arithmetic mean fitness. In this paper we illustrate the concept of geometric mean fitness in a few simple models. We discuss its implications for the adaptive evolution of phenotypes, e.g. foraging under predation risks and clutch size. Next, we present an application: the risk-spreading egg-laying behaviour of the cabbage white butterfly, and develop a two-patch population dynamic model to show how the optimal solution diverges from the ssual arithmetic mean approach. The dynamics of these stochastic models cannot be predicted from the dynamics of simple deterministic models. Thus the inclusion of stochastic factors in the analyses of populations is essential to the understanding of not only population dynamics, but also their evolutionary dynamics.