Flexible spatio-temporal stationary variogram models

In this paper we propose a generalization of the Shapiro and Botha (1991) approach that allows one to obtain flexible spatio-temporal stationary variogram models. It is shown that if the weighted least squares criterion is chosen, the fitting of such models to pilot estimations of the variogram can be easily carried out by solving a quadratic programming problem. The work also includes an application to real data and a simulation study in order to illustrate the performance of the proposed space-time dependency modeling.     

Book Review: Organizing Women in Contemporary Russia: Engendering Transition,Valerie Sperling,Cambridge University Press,Cambridge, UK, 1999

VOLUNTAS: International Journal of Voluntary and Nonprofit Organizations -     

Projected spending on pensions in Spain: A viability analysis

The viability of pay-as-you-go retirement pension schemes, such as that of Spain, remains a subject of ongoing debate. In this article we shall attempt to demonstrate that demography is the key variable that determines a system's viability. Analysis of several predictive studies conducted in the country shows that many of their predictions have been erroneous and their findings overpessimistic. This is because their forecasts were based on projections for the resident population, and overlooked the magnitude of the recent phenomenon of immigration. If the current influx of migrants continues, the problem of viability can be resolved.     

A class of stochastic epidemic models and its deterministic counterpart

A general stochastic model for the spread of an epidemic developing in a closed population is introduced. Each model consisting of a discrete-time Markov chain involves a deterministic counterpart represented by an ordinary differential equation. Our framework involves various epidemic models such as a stochastic version of the Kermack and McKendrick model and the SIS epidemic model. We prove the asymptotic consistency of the stochastic model regarding a deterministic model; this means that for a large population both modelings are similar. Moreover, a Central Limit Theorem for the fluctuations of the stochastic modeling regarding the deterministic model is also proved.     

The impact of the board of directors characteristics on corporate performance and risk-taking before and during the global financial crisis

Over recent years, the effectiveness of good corporate governance practices has received considerable attention by the financial literature. In the current global finance crisis, several practitioners, academic and regulators argue that mechanisms of corporate governance have not served their purpose to safeguard equitably the interest of stakeholders, increasing the corporate risk-taking without proper management. This research contributes to the empirical literature, analyzing the impact of board characteristics and the capital structure on corporate performance and corporate risk-taking, in two different economic contexts: in an economic growth and in an economic recession. The methodology implemented takes into account the bidirectional causality and addresses endogeneity problem using a simultaneous equations system with three-stage least squares estimation method. The results show that the effectiveness of the board is sensitive to the economic period and the capital structure leads to reduce the levels of corporate risk-taking during the crisis. This research suggests that good corporate governance mechanisms should mitigate excessive corporate risk-taking and protect the interest of stakeholders in both periods: before and during the global financial crisis.     

The pseudo‐GEE approach to the analysis of longitudinal surveys

Longitudinal surveys have emerged in recent years as an important data collection tool for population studies where the primary interest is to examine population changes over time at the individual level. Longitudinal data are often analyzed through the generalized estimating equations (GEE) approach. The vast majority of existing literature on the GEE method; however, is developed under non‐survey settings and are inappropriate for data collected through complex sampling designs. In this paper the authors develop a pseudo‐GEE approach for the analysis of survey data. They show that survey weights must and can be appropriately accounted in the GEE method under a joint randomization framework. The consistency of the resulting pseudo‐GEE estimators is established under the proposed framework. Linearization variance estimators are developed for the pseudo‐GEE estimators when the finite population sampling fractions are small or negligible, a scenario often held for large‐scale surveys. Finite sample performances of the proposed estimators are investigated through an extensive simulation study using data from the National Longitudinal Survey of Children and Youth. The results show that the pseudo‐GEE estimators and the linearization variance estimators perform well under several sampling designs and for both continuous and binary responses. The Canadian Journal of Statistics 38: 540–554; 2010 © 2010 Statistical Society of Canada     

Talk about Money. Studying the Interaction between Social Worker and Client

During the last two decades there has been an increase in the number of studies, especially in the Nordic countries, of the talk between social worker and client. This paper presents an overview of these studies. The focus of many of the studies has been the transformation of a private citizen with a personal financial problem into a client with an institutionally legitimate financial problem. This transformation process is mainly effected in the conversation between social worker and client.     

Racial differences in physician usage among the elderly poor in the United States

Despite the rapidly growing ranks of the elderly in America, the increasing racial and ethnic diversity of this population, and the large number of seniors who are poor, there are relatively few systematic investigations that examine the causes of racial differences in health care use specifically among elders living in poverty. This article addresses this issue by examining differences in patterns of having and using a physician among the elderly poor, the role that race plays and what might explain it. We demonstrate that even within this disadvantaged and medically engaged population there are persistent and significant racial differences in having and using a doctor. Specifically, we show: (1) Whites and women are more likely to have a regular doctor than men and African Americans; (2) Among those who have a doctor, whites and women also visit the doctor with greater frequency than other groups even at the same levels of health or illness; (3) After accounting for the varying levels and effects of social connectedness, racial differences in having a doctor essentially disappear; and (4) While differences in having a regular doctor can be accounted for using measures of social connectedness, substantial and robust racial and gender differences in doctor use remain. In the end, we provide an analysis that examines typical factors known to influence health care use, and find that while need, structural factors, perceptions of care, and social connectedness have a powerful effect on doctor visits, the racial variation in using a doctor cannot be explained away with the available measures.     

Partially linear models and their applications to change point detection of chemical process data

In many chemical data sets, the amount of radiation absorbed (absorbance) is related to the concentration of the element in the sample by Lambert–Beer's law. However, this relation changes abruptly when the variable concentration reaches an unknown threshold level, the so-called change point. In the context of analytical chemistry, there are many methods that describe the relationship between absorbance and concentration, but none of them provide inferential procedures to detect change points. In this paper, we propose partially linear models with a change point separating the parametric and nonparametric components. The Schwarz information criterion is used to locate a change point. A back-fitting algorithm is presented to obtain parameter estimates and the penalized Fisher information matrix is obtained to calculate the standard errors of the parameter estimates. To examine the proposed method, we present a simulation study. Finally, we apply the method to data sets from the chemistry area. The partially linear models with a change point developed in this paper are useful supplements to other methods of absorbance–concentration analysis in chemical studies, for example, and in many other practical applications.