Use of Markov Chain Monte Carlo Analysis with a Physiologically-Based Pharmacokinetic Model of Methylmercury to Estimate Exposures in U.S. Women of Childbearing Age

A Bayesian approach, implemented using Markov Chain Monte Carlo (MCMC) analysis, was applied with a physiologically‐based pharmacokinetic (PBPK) model of methylmercury (MeHg) to evaluate the variability of MeHg exposure in women of childbearing age in the U.S. population. The analysis made use of the newly available National Health and Nutrition Survey (NHANES) blood and hair mercury concentration data for women of age 16–49 years (sample size, 1,582). Bayesian analysis was performed to estimate the population variability in MeHg exposure (daily ingestion rate) implied by the variation in blood and hair concentrations of mercury in the NHANES database. The measured variability in the NHANES blood and hair data represents the result of a process that includes interindividual variation in exposure to MeHg and interindividual variation in the pharmacokinetics (distribution, clearance) of MeHg. The PBPK model includes a number of pharmacokinetic parameters (e.g., tissue volumes, partition coefficients, rate constants for metabolism and elimination) that can vary from individual to individual within the subpopulation of interest. Using MCMC analysis, it was possible to combine prior distributions of the PBPK model parameters with the NHANES blood and hair data, as well as with kinetic data from controlled human exposures to MeHg, to derive posterior distributions that refine the estimates of both the population exposure distribution and the pharmacokinetic parameters. In general, based on the populations surveyed by NHANES, the results of the MCMC analysis indicate that a small fraction, less than 1%, of the U.S. population of women of childbearing age may have mercury exposures greater than the EPA RfD for MeHg of 0.1 μg/kgg/day, and that there are few, if any, exposures greater than the ATSDR MRL of 0.3 μgg/kgg/day. The analysis also indicates that typical exposures may be greater than previously estimated from food consumption surveys, but that the variability in exposure within the population of U.S. women of childbearing age may be less than previously assumed.     

Understanding Community Resilience from a PRA Perspective Using Binary Decision Diagrams

Probabilistic risk assessment (PRA) is a useful tool to assess complex interconnected systems. This article leverages the capabilities of PRA tools developed for industrial and nuclear risk analysis in community resilience evaluations by modeling the food security of a community in terms of its built environment as an integrated system. To this end, we model the performance of Gilroy, CA, a moderate‐size town, with regard to disruptions in its food supply caused by a severe earthquake. The food retailers of Gilroy, along with the electrical power network, water network elements, and bridges are considered as components of a system. Fault and event trees are constructed to model the requirements for continuous food supply to community residents and are analyzed efficiently using binary decision diagrams (BDDs). The study also identifies shortcomings in approximate classical system analysis methods in assessing community resilience. Importance factors are utilized to rank the importance of various factors to the overall risk of food insecurity. Finally, the study considers the impact of various sources of uncertainties in the hazard modeling and performance of infrastructure on food security measures. The methodology can be applicable for any existing critical infrastructure system and has potential extensions to other hazards.     

Chaos: A Challenge to Refine Systems Theory

Chaos theory may have relevance to marital and family therapy. Some connections are tentatively explored.     

Perceived importance of “social goals” in business organizations

Business organizations operate within a complex socio-technical environment. Interactions between these socio-technical dimensions and the managers' personal value systems are thought to influence managerial role patterns and decisions. This paper investigates shifts in perceived importance of “social goals” from a set of organizational goals. The research concludes that there has been no significant changes occurring in either the ordering or the clustering of organizational goals.     

Fear of people with mental illnesses: the role of personal and impersonal contact and exposure to threat or harm

Vignette and laboratory experiments suggest that negative reactions to people with mental illness are a direct consequence of their symptomatic behavior, but because of their poor external validity, these studies cannot tell us whether widespread negative public reactions to people with mental illness actually result from observation of symptomatic behavior. Focusing on perceived danger, we use a large national survey to test the "behavior hypothesis" in the general population. We reason that, if this hypothesis is correct, contact with people with mental illnesses should be associated with more perceived danger, and exposure to threat or harm should mediate this association. On the contrary, respondents with more personal and impersonal contact perceive people with mental illness to be less dangerous. Exposure to threat is more common among people with more contact, but this exposure explains very little of the variance in perceived danger. These findings do not support the conclusion that public fear of people with mental illness is due to the observation of violent behavior.     

The production of understanding

While there is little doubt that sociological theory and research has had an important impact on the way people think about health and health care, mental health and medical sociologists are often confronted with challenges concerning the utility of the work that they do. Among the doubters are deans, funding agencies and family members. We are challenged by the ascendency of biological interpretations of human behaviors, by the incompatibility between the contextual view we prefer and the very strong individualistic orientation of our culture, and by the fact that we do not have an applied arm that trains the professionals who treat health and mental-health conditions. How do we respond to this challenge? The title of this paper gives a short answer: "The Production of Understanding." I propose that a powerful but under-recognized value of our work is the generation of explanations about health and mental health matters that help people understand the other side of an "us"/"them" divide. We produce understanding in a context in which misunderstanding is regularly constructed by powerful people who offer victim-blaming explanations for the circumstances experienced by people with less power. The production of understanding serves as an important counterbalance to this tendency. Our work shapes the way people think about problems related to health and mental health, limits the power of inaccurate victim-blaming accounts and provides understanding about why health and mental health are mal-distributed among people from different social circumstances.     

Leadership efficacy: Review and future directions

The concept of leader efficacy has received relatively little attention in the leadership literature. This is somewhat surprising given that effective leadership requires high levels of agency (i.e., deliberately or intentionally exerting positive influence) and confidence. This review uses existing theory and research on leader efficacy as a point of departure for proposing an expanded and multi-level framework for understanding the domain of leadership efficacy that includes leader, follower, and collective efficacies. The primary goals are to provide a conceptual framework to stimulate future theory and research on building efficacious leadership and to understand how such leadership develops and has implications for effective performance.     

A Decision Framework for Managing Risk to Airports from Terrorist Attack

This article presents an asset‐level security risk management framework to assist stakeholders of critical assets with allocating limited budgets for enhancing their safety and security against terrorist attack. The proposed framework models the security system of an asset, considers various threat scenarios, and models the sequential decision framework of attackers during the attack. Its novel contributions are the introduction of the notion of partial neutralization of attackers by defenders, estimation of total loss from successful, partially successful, and unsuccessful actions of attackers at various stages of an attack, and inclusion of the effects of these losses on the choices made by terrorists at various stages of the attack. The application of the proposed method is demonstrated in an example dealing with security risk management of a U.S. commercial airport, in which a set of plausible threat scenarios and risk mitigation options are considered. It is found that a combination of providing blast‐resistant cargo containers and a video surveillance system on the airport perimeter fence is the best option based on minimum expected life‐cycle cost considering a 10‐year service period.