Markov-modulated infinite-server queues driven by a common background process

This paper studies a system with multiple infinite-server queues that are modulated by a common background process. If this background process, being modeled as a finite-state continuous-time Markov chain, is in state j, then the arrival rate into the i-th queue is λ_{i, j}, whereas the service times of customers present in this queue are exponentially distributed with mean μ^{? 1}_{i, j}; at each of the individual queues all customers present are served in parallel (thus reflecting their infinite-server nature).

Three types of results are presented: in the first place (i) we derive differential equations for the probability-generating functions corresponding to the distributions of the transient and stationary numbers of customers (jointly in all queues), then (ii) we set up recursions for the (joint) moments, and finally (iii) we establish a central limit theorem in the asymptotic regime in which the arrival rates as well as the transition rates of the background process are simultaneously growing large.     

Personal Identity Processes from Adolescence Through the Late 20s: Age Trends,Functionality, and Depressive Symptoms

Personal identity formation constitutes a crucial developmental task during the teens and 20s. Using a recently developed five‐dimensional identity model, this cross‐sectional study (N = 5834) investigated age trends from ages 14 to 30 for different commitment and exploration processes. As expected, results indicated that, despite some fluctuations over time, commitment processes tended to increase in a linear fashion. Exploration in breadth and exploration in depth were characterized by quadratic trends, with the highest levels occurring in emerging adulthood. Further, the functionality of these identity processes, and especially of exploration, changed over time. Exploration in breadth and exploration in depth were strongly related to commitment processes especially in adolescence and emerging adulthood, but these exploration processes became increasingly associated with ruminative exploration and depressive symptoms in the late 20s. Theoretical implications and suggestions for future research are outlined.     

The redistributive effect of public and private social programmes: A cross‐country empirical analysis

A function of many national social protection systems is to substantially redistribute income. However, the size and nature of social protection programmes are changing. In a number of countries there has been a shift from public towards private social protection arrangements, with the latter substituting for, or complementing, public programmes. Developing earlier work, this present article analyses the redistributive impact on income of public versus private social protection programmes. Using recent data from the Organisation for Economic Co‐operation and Development, we find a strong positive relationship between public social expenditures and income redistribution across countries. For private social expenditures, we find a weak, but statistically significant, negative relationship with the level of redistribution. In countries where a larger share of total social expenditure is accorded to private arrangements there is less income redistribution. We conclude that the choice between the relative weight of public and private provision of social protection affects the redistributive impact of the welfare state.     

The Influence of Men��s Income and Employment on Marriage and Cohabitation: Testing Oppenheimer��s Theory in Europe

This article discusses Oppenheimer's theory on marriage timing, reviews the way this theory was received in European demography and family sociology, and develops a new test of the theory using annual panel data from 13 European countries for the period 1994-2001. Several indicators of men's economic status are used, including school enrollment, employment, type of labor contract, work experience, income, and education. Effects of these indicators are estimated for the transition to marriage and cohabitation, as well as for the transition from cohabitation to marriage. Country differences in these effects are examined as well. The evidence provides strong support for the male breadwinner hypothesis on the one hand, and for Oppenheimer's career uncertainty hypothesis on the other. However, the relevance of these hypotheses also depends on the national context, and especially on the way gender roles are divided in a society.     

Identification of Salmonella high risk pig-herds in Belgium by using semiparametric quantile regression

Summary.  Consumption of pork that is contaminated with Salmonella is an important source of human salmonellosis world wide. To control and prevent salmonellosis, Belgian pig-herds with high Salmonella infection burden are encouraged to take part in a control programme supporting the implementation of control measures. The Belgian government decided that only the 10% of pig-herds with the highest Salmonella infection burden (denoted high risk herds) can participate. To identify these herds, serological data reported as sample-to-positive ratios (SP-ratios) are collected. However, SP-ratios have an extremely skewed distribution and are heavily subject to confounding seasonal and animal age effects. Therefore, we propose to identify the 10% high risk herds by using semiparametric quantile regression with P -splines. In particular, quantile curves of animal SP-ratios are estimated as a function of sampling time and animal age. Then, pigs are classified into low and high risk animals with high risk animals having an SP-ratio that is larger than the corresponding estimated upper quantile. Finally, for each herd, the number of high risk animals is calculated as well as the beta–binomial p -value reflecting the hypothesis that the Salmonella infection burden is higher in that herd compared with the other herds. The 10% pig-herds with the lowest p -values are then identified as high risk herds. In addition, since high risk herds are supported to implement control measures, a risk factor analysis is conducted by using binomial generalized linear mixed models to investigate factors that are associated with decreased or increased Salmonella infection burden. Finally, since the choice of a specific upper quantile is to a certain extent arbitrary, a sensitivity analysis is conducted comparing different choices of upper quantiles.     

The Effect of Children on Men’s and Women’s Chances of Re-partnering in a European Context

This work examines what role children play in the re-partnering process in five European countries (Norway, France, Germany, Romania, and the Russian Federation) by addressing the following research questions: (1) To what extent do men and women differ in their re-partnering chances?; (2) Can gender differences in re-partnering be explained by the presence of children?; (3) How do the custodial arrangements and the child’s age affect the re-partnering chances of men and women? We use the partnership and parenthood histories of the participants in the first wave of the Generations and Gender Survey (United Nations, Generations and Gender Programme: Survey Instruments. United Nations, New York/Geneva, 2005) to examine the transition to moving in with a new partner following the dissolution of the first marital union, separately for men and women. The story that emerges is one of similarities in the effects rather than differences. In most countries, men are more likely to re-partner than women. This gender difference can be attributed to the presence of children as our analyses show that childless men and women do not differ in their probability to re-partner. Mothers with resident children are less likely to re-partner than non-mothers and a similar though often non-significant effect of resident children is observed for fathers. In most countries we find that as the child ages, the chances to enter a new union increase. In sum, our study indicates that children are an important factor in re-partnering and a contributor to the documented gender gap in re-partnering, and this holds throughout distinct institutional and cultural settings.