Ultrastructural elliptical models

Dolby's (1976) ultrastructural model with no replications is investigated within the class of the elliptical distributions. General asymptotic results are given for the sample covariance matrix S in the presence of incidental parameters. These results are used to study the asymptotic behaviour of some estimators of the slope parameter, unifying and extending existing results in the literature. In particular, under some regularity conditions they are shown to be consistent and asymptotically normal. For the special case of the structural model, some asymptotic relative efficiencies are also reported which show that generalized least squares and the method of moment estimators can be highly inefficient under nonnormality.     

Modelling the management of underground water assets

Central to the activities of any industry is the modernization of its assets. This paper describes the application of statistical methods to the asset management plan of a large water company. A model for the underground assets is given in detail, and the extensive computations required are illustrated. A Bayesian model shows the consequences of various policy options and provides realistic measures of the uncertainty connected with them.     

History of sexual abuse and parental alcohol misuse: Risk,outcomes and protective factors in adolescents

This study examined the school performance, suicidal involvement, disordered eating behaviors, pregnancy risk and chemical use of teenagers with a history of sexual abuse or parental alcohol misuse and found that they had higher rates of these adverse outcomes than among a comparison group of teenagers without such background risk factors. Adolescents with dual-risk background reported higher levels of suicide risk, disordered eating, sexual behaviors and chemical abuse than teenagers with only one background risk factor. Among index group members, protective factors against these adverse outcomes included a high degree of religiosity and the ability to discuss problems with family or friends. Risk factors that increased the likelihood of adverse outcomes included depression, perceived substance use in school and worries about family financial security.The first author was supported in the preparation of this article by a grant from the Lois and Samuel Silberman Fund of New York.     

ALTRUISM, MATCHING, AND NONMARKET INSURANCE

Incomplete market insurance gives rise to nonmarket arrangements for coinsurance. We find that the effort altruistically linked individuals take to avoid an accident increases with the degree of altruism. If the degree of altruism is sufficiently high, an economy with nonmarket insurance yields higher social welfare than an economy without nonmarket insurance. As altruism increases, the equilibrium level of effort approaches the second-best solution without the need for costly monitoring. Coinsurance is above (below) the socially optimal level if individuals place greater weight (less weight) on their own utility than on that of their partners.     

The Effect of Gender Context on Children's Social Behavior in a Limited Resource Situation: An Observational Study

Knowing when to compete and when to cooperate to maximize opportunities for equal access to activities and materials in groups is critical to children's social and cognitive development. The present study examined the individual (gender, social competence) and contextual factors (gender context) that may determine why some children are more successful than others. One hundred and fifty‐six children (M age=6.5 years) were divided into 39 groups of four and videotaped while engaged in a task that required them to cooperate in order to view cartoons. Children within all groups were unfamiliar to one another. Groups varied in gender composition (all girls, all boys, or mixed‐sex) and social competence (high vs. low). Group composition by gender interaction effects were found. Girls were most successful at gaining viewing time in same‐sex groups, and least successful in mixed‐sex groups. Conversely, boys were least successful in same‐sex groups and most successful in mixed‐sex groups. Similar results were also found at the group level of analysis; however, the way in which the resources were distributed differed as a function of group type. Same‐sex girl groups were inequitable but efficient whereas same‐sex boy groups were more equitable than mixed groups but inefficient compared to same‐sex girl groups. Social competence did not influence children's behavior. The findings from the present study highlight the effect of gender context on cooperation and competition and the relevance of adopting an unfamiliar peer paradigm when investigating children's social behavior.     

A Risk-Based Approach to Setting Priorities in Protecting Bridges Against Terrorist Attacks

This article presents an approach to the problem of terrorism risk assessment and management by adapting the framework of the risk filtering, ranking, and management method. The assessment is conducted at two levels: (1) the system level, and (2) the asset-specific level. The system-level risk assessment attempts to identify and prioritize critical infrastructures from an inventory of system assets. The definition of critical infrastructures offered by Presidential Decision Directive 63 was used to determine the set of attributes to identify critical assets--categorized according to national, regional, and local impact. An example application is demonstrated using information from the Federal Highway Administration National Bridge Inventory for the State of Virginia. Conversely, the asset-specific risk assessment performs an in-depth analysis of the threats and vulnerabilities of a specific critical infrastructure. An illustration is presented to offer some insights in risk scenario identification and prioritization, multiobjective evaluation of management options, and extreme-event analysis for critical infrastructure protection.     

De-standardization of Family-Life Trajectories of Young Adults: A Cross-National Comparison Using Sequence Analysis

We introduce a number of new methods based on sequence analysis to test hypotheses on the de-standardization of family-life trajectories in early adulthood, using Fertility and Family Survey data on 19 countries. Across cohorts, family-life trajectories of young adults have not become more turbulent. However, in most countries family-life trajectories of young adults have become less similar to one another and the variation in the types of family-trajectories has increased. Contrary to expectations, no clear differences in de-standardization were observed between countries characterized by a social-democratic welfare-state regime and countries characterized by either liberal or conservative welfare-state regimes.     

QUANTILES OF SUMS AND EXPECTED VALUES OF ORDERED SUMS

Watson & Gordon (1986) investigated the relationship between the quantiles of a sum of independent continuous random variables and the sum of the individual quantiles. In this note some further results are obtained. Also corresponding relationships are developed for the expected values of the order statistics of a sum, and for the sum of the expected values of the individual order statistics.