Choice correspondences for public goods

We consider collective choice problems where a group of agents has to decide on the location of a public facility in a Euclidean space. A well-known solution for such problems is the coordinatewise median of the reported votes and additional fixed ballots. Instead of adding ballots, we extend the median solution by allowing set-valued outcomes. This especially applies for location problems with an even number of agents. Received: 14 August 1998/Accepted: 29 August 2000     

Matrimonial circuits in kinship networks: Calculation, enumeration and census

The article presents a series of new methods for analyzing the morphology of kinship networks via the study of matrimonial circuits (closed chains of kinship and marriage ties). The article gives a simple definition of matrimonial circuits in mixed graphs and introduces the technique of representing matrimonial circuit types by characteristic vectors. This technique is used to develop (1) an arithmetic approach to the algebra of circuit composition, (2) a method for the complete enumeration of matrimonial circuit types, and (3) an algorithm for finding and counting matrimonial circuits in empirical kinship networks. All methods have been implemented in the software Puck (Program for the Use and Computation of Kinship Data).     

Inference Under Heteroskedasticity and Leveraged Data

We evaluate the finite-sample behavior of different heteros-ke-das-ticity-consistent covariance matrix estimators, under both constant and unequal error variances. We consider the estimator proposed by Halbert White (HC0), and also its variants known as HC2, HC3, and HC4; the latter was recently proposed by Cribari-Neto (2004 Cribari-Neto , F. ( 2004 ). Asymptotic inference under heteroskedasticity of unknown form . Computat. Statist. Data Anal. 45 : 215 – 233 .[Crossref], [Web of Science ®] , [Google Scholar]). We propose a new covariance matrix estimator: HC5. It is the first consistent estimator to explicitly take into account the effect that the maximal leverage has on the associated inference. Our numerical results show that quasi-t inference based on HC5 is typically more reliable than inference based on other covariance matrix estimators.     

Maximum Likelihood Inference for Multivariate Frailty Models Using an Automated Monte Carlo EM Algorithm

We present a maximum likelihood estimation procedure for the multivariate frailty model. The estimation is based on a Monte Carlo EM algorithm. The expectation step is approximated by averaging over random samples drawn from the posterior distribution of the frailties using rejection sampling. The maximization step reduces to a standard partial likelihood maximization. We also propose a simple rule based on the relative change in the parameter estimates to decide on sample size in each iteration and a stopping time for the algorithm. An important new concept is acquiring absolute convergence of the algorithm through sample size determination and an efficient sampling technique. The method is illustrated using a rat carcinogenesis dataset and data on vase lifetimes of cut roses. The estimation results are compared with approximate inference based on penalized partial likelihood using these two examples. Unlike the penalized partial likelihood estimation, the proposed full maximum likelihood estimation method accounts for all the uncertainty while estimating standard errors for the parameters.     

A New Agenda for European Charity: Catholic Welfare and Organizational Change in France and Germany

Case study research from France and Germany reveals that Catholic welfare is revising its mission and its methods. Central points are a different approach to voluntary participation, new public relations, and a rearrangement of public-private partnerships. As a result, Catholic welfare has become activated in both countries. While the shrinking of the overall influence of Catholic charity seems inevitable, there is more creative agency, and less programming by the old stakeholders. The national paths of change, however, differ in that Caritas, defending its service approach, is confronted with a process of de-institutionalization while Secours catholique, though giving particular emphasis to voluntary action is entering into further institutionalization.     

Maintaining your immune system--one method for enhanced longevity

The immune system is an important evolutionary invention to battle invaders in young and old organisms. Successful aging in humans who achieve nonagenarian status and beyond depends on how the immune system changes over time. Whether certain immune parameters vary with increased age is influenced by the genotype and lifestyle of the individual.