Principles of Good Practice for the Use of Monte Carlo Techniques in Human Health and Ecological Risk Assessments

We propose 14 principles of good practice to assist people in performing and reviewing probabilistic or Monte Carlo risk assessments, especially in the context of the federal and state statutes concerning chemicals in the environment. Monte Carlo risk assessments for hazardous waste sites that follow these principles will be easier to understand, will explicitly distinguish assumptions from data, and will consider and quantify effects that could otherwise lead to misinterpretation of the results. The proposed principles are neither mutually exclusive nor collectively exhaustive. We think and hope that these principles will evolve as new ideas arise and come into practice.     

Solving the part families problem in discrete-parts manufacture by simulated annealing

In the production planning and control of discrete-parts manufacture, aggregation of parts into families, on the basis of similarity, is carried out to ease both long-horizon planning and short-horizon scheduling. Additional advantages are related to those of group technology (GT), such as simplifying the flow of parts and tools and reducing both set-up and production costs. The problem of formally forming part families is presented and discussed. Previous work is reviewed and assessed. Two solution approaches, one based on a location model, the other on simulated annealing, are presented and compared along with test results. The location formulation, which results in an integer programming model solved by Lagrangian relaxation, proved capable of producing solutions of excellent quality, but only for relatively small problem instances. In contrast, simulated annealing, which is a general heuristic approach to combinatorial optimization, produced solutions of comparable quality and could handle realistically large problem instances. However, careful design of the simulated annealing algorithm is crucially important. An effective design is presented.     

Family transitions in Young Adulthood

Using the first (1995) and third (2001-2002) waves of the Add Health survey, we examine women 's family transitions up to age 24. Only a third of all women marry, and a fifth of those marriages dissolve before age 24. Three out of eight women have afirst birth, with a substantial majority of those births outside of marriage: 66% for whites, 96% for blacks, and 72% for Mexican Americans. Cohabitation is the predominant union form; 59% of women cohabit at least once by age 24. Most cohabitations are short lived, with approximately one in five resulting in a marriage. We summarize the family and relationship experience of women up to age 24 in terms offour categories, each accounting for roughly a quarter of all women. Category 1 has the women who remain single nonparents. Category 2 has the early marriers, women whose marriage is not preceded by a first birth. Category 3 has those who become single parents. Category 4 has the women who cohabit at least once, but who do not marry or have a birth by age 24. The strictly ordered transitions of the 1950s are long gone and have been replaced by a variety of paths to adulthood.     

Colourism and African–american wealth: evidence from the nineteenth-century south

Black is not always black. Subtle distinctions in skin tone translate into significant differences in outcomes. Data on more than 15,000 households interviewed during the 1860 US federal census exhibit sharp differences in wealth holdings between white, mulatto, and black households in the urban South. We document these differences, investigate relationships between wealth and recorded household characteristics, and decompose the wealth gaps to examine the returns to racial characteristics. The analysis reveals a distinct racial hierarchy. Black wealth was only 20% of white wealth, but mulattoes held nearly 50% of whites’ wealth. This advantage is consistent with colourism, the favouritism shown to those of lighter complexion.

College students’ attitudes toward abortion and commitment to the issue

Male and female participants were surveyed on abortion attitudes, commitment, and abortion experience. Results revealed a normal distribution of abortion attitudes rejecting the notion that the vast majority of the sample would have significantly pro-choice views. No significant difference was found in overall abortion attitudes of males vs. females, however, individuals with direct abortion experience were found to have significantly stronger pro-choice attitudes than individuals without direct abortion experience. Overall, college students reported a moderate degree of commitment to the issue of abortion. Females were significantly more committed than males, individuals with direct abortion experience were significantly more committed than individuals without direct abortion experience, and individuals with more extreme abortion attitudes were significantly more committed than those with weaker, more ambivalent, attitudes. No significant difference was found in level of commitment between pro-choice and pro-life individuals.     

Factors influencing Soay sheep survival

We present a survival analysis of Soay sheep mark recapture and recovery data. Unlike previous conditional analyses, it is not necessary to assume equality of recovery and recapture probabilities; instead these are estimated by maximum likelihood. Male and female sheep are treated separately, with the higher numbers and survival probabilities of the females resulting in a more complex model than that used for the males. In both cases, however, age and time aspects need to be included and there is a strong indication of a reduction in survival for sheep aged 7 years or more. Time variation in survival is related to the size of the population and selected weather variables, by using logistic regression. The size of the population significantly affects the survival probabilities of male and female lambs, and of female sheep aged 7 or more years. March rainfall and a measure of the North Atlantic oscillation are found to influence survival significantly for all age groups considered, for both males and females. Either of these weather variables can be used in a model. Several phenotypic and genotypic individual covariates are also fitted. The only covariate which is found to influence survival significantly is the type of horn of first-year female sheep. There is a substantial variation in the recovery probabilities over time, reflecting in part the increased effort when a population crash was expected. The goodness of fit of the model is checked by using graphical procedures.     

Binary probability maps using a hidden conditional autoregressive Gaussian process with an application to Finnish common toad data

The Finnish common toad data of Heikkinen and Hogmander are reanalysed using an alternative fully Bayesian model that does not require a pseudolikelihood approximation and an alternative prior distribution for the true presence or absence status of toads in each 10 km×10 km square. Markov chain Monte Carlo methods are used to obtain posterior probability estimates of the square-specific presences of the common toad and these are presented as a map. The results are different from those of Heikkinen and Hogmander and we offer an explanation in terms of the prior used for square-specific presence of the toads. We suggest that our approach is more faithful to the data and avoids unnecessary confounding of effects. We demonstrate how to extend our model efficiently with square-specific covariates and illustrate this by introducing deterministic spatial changes.     

Suicide and mental health problems among Swedish youth in the wake of the 1990s recession

The purpose of this explorative study is to bring together a variety of Swedish data sources with indicators of youth mental health and living conditions in order to illuminate trends during the last decades, elucidate possible determinants of mental ill health and develop hypotheses to explain the observed trend patterns. The analyses in the study reveal some surprising inconsistencies with respect to the mental health trends among young people during the 1990s. Most striking is the pattern of increasing youth unemployment coinciding with almost inverse trends in the rates of suicide. The secular trends in fatal suicides during this period do not show any increase but some actual decrease in sub‐populations despite high sustained levels of unemployment. In contrast, survey data indicate that the general mental health of youth during this period appears to have deteriorated.     

Analysis of Competing Risks by Using Bayesian Smoothing

We consider the competing risks set-up. In many practical situations, the conditional probability of the cause of failure given the failure time is of direct interest. We propose to model the competing risks by the overall hazard rate and the conditional probabilities rather than the cause-specific hazards. We adopt a Bayesian smoothing approach for both quantities of interest. Illustrations are given at the end.     

On the functional form of corporate cooptation: Empirical findings linking the intensity of market constraint with the frequency of directorate ties

Using data on market transactions involving manufacturing industries in the 1967 American economy and data on directors of large firms involved in manufacturing at the time, the frequency of interorganizational ties through corporate directorates operating in economic sectors J and M is shown to increase with the extent to which average profits in industry J are constrained by its market transactions (sales and/or purchases) with sector M. Market constraint has its strongest and most direct effect on the spread of a corporation through ownership ties into multiple sectors rather than on the corporation's use of interlocking. However, the central point demonstrated concerns directorate tie frequency. Not only is the absence of directorate ties predicted by the absence of market constraint, the actual frequency of ties between economic sectors is predicted by the intensity of market constraint they constitute for one another's profits.