Single-Index-Based CoVaR With Very High-Dimensional Covariates

Systemic risk analysis reveals the interdependencies of risk factors especially in tail event situations. In applications the focus of interest is on capturing joint tail behavior rather than a variation around the mean. Quantile and expectile regression are used here as tools of data analysis. When it comes to characterizing tail event curves one faces a dimensionality problem, which is important for CoVaR (Conditional Value at Risk) determination. A projection-based single-index model specification may come to the rescue but for ultrahigh-dimensional regressors one faces yet another dimensionality problem and needs to balance precision versus dimension. Such a balance is achieved by combining semiparametric ideas with variable selection techniques. In particular, we propose a projection-based single-index model specification for very high-dimensional regressors. This model is used for practical CoVaR estimates with a systemically chosen indicator. In simulations we demonstrate the practical side of the semiparametric CoVaR method. The application to the U.S. financial sector shows good backtesting results and indicate market coagulation before the crisis period. Supplementary materials for this article are available online.     

The use of Information and Communication Technology (ICT) in the rehabilitation of individuals with severe functional impairments in a municipal care service system

This article explores the development of a scheme to use Information and Communication Technology (ICT) in the training of individuals with severe functional impairments. Computers were used as an integral part of a rehabilitation programme for training, and the authors found that the resource was a useful addition to other treatment methods. This article describes the development and subsequent setting up of computers for training and how the study progressed. The study used a somewhat unique bottom up approach that first trained care-giving staff in computer skills. The caregivers in turn worked with and trained some of those they served. This learning strategy drew upon the concept of learning, empowerment and the motivation of all involved in a system and process. The study found that by using ICT all involved felt a greater sense of empowerment and improvement in the quality of life. That caregivers were involved at all stages was valuable in that they felt an ownership of the process and that they also benefited from being involved because they also learned new skills.     

On the Use of the Cause Table in Handling Common Cause Events in System Analysis

A method is presented for applying the cause table concept to the problem of common cause events. This method can be regarded as an alternative to the approach in which these events are included directly into the system fault trees. In comparison with this approach, the cause table method offers the advantage of simple fault trees, convenient visibility of the contributions of causes, and the ability to truncate the numerical calculation conveniently by aggregating small terms into an "other" category. Generally speaking, the cause table method can be said to handle common causes at the level of arithmetic (i.e., numbers) rather than at the level of algebra (determining cutsets and frequency equations).     

Statistical aspects of W. D. Fisher's method of optimal aggregation

W. D. Fisher's approach to approximating a known linear model y=Ax by an aggregation-disaggregation sequence involves a moment matrix M which is supposed to be known. This paper investigates the statistical problems arising when M is not known. As an example we consider the open static Leontief model with A being the Leontief inverse. Under the assumption that the exogenous variables are multinormal with zero mean, tests and confidence intervals for the loss of information are given. The use of maximum entropy estimation of M for insufficient data is discussed. Statistical procedures to evaluate the goodness of aggregation-disaggregation of a time series of matrices A are also described.     

Book reviews

Qualitative Sociology -     

Positions,Roles, and Dependencies in a Community Interorganization System*

This study focuses on community structure as a network of interorganizational linkages, with an eye toward (1) generating new conceptual schemes to study the community as a social network and (2) developing a methodology to measure new dimensions of community structure. An analysis of structurally equivalent roles is performed in two communities for three organizational resource networks: money, information, and moral support. Global dependencies on resource generator, consumer, and transmitter roles for the money network are analyzed using loglinear models. Local dependencies within the money network are also examined. Finally, the study examines the perceived influence of organizations in community affairs as a function of the organizations' global positions within the community network.     

In memoriam Ernst Topitsch (20.03.1919–26.01.2003)

Ohne Zusammenfassung