Step-through simulation

This report describes the initial development of the Step-Through variant of Monte Carlo simulation, a new procedure for implementing decision analysis or for training decision makers. Like regular Monte Carlo simulation, it involves sampling possible aftermaths of an initial action, and generating a distribution of outcome values for it. However, the detailed structure and/or assessments of the decision model are elicited as called for in the execution of each trial. It, therefore, permits substantial economy of elicitation if there are few trials. The Step-Through procedure also offers economy of elicitation and calculation over a traditional extensive tree decision-analytic model without requiring simplifications or aggregations in the model's conceptualization. In addition to describing this procedure, this paper presents the results of a preliminary test and evaluation of its viability.     

Development and the environment: Managing the contradictions?

The United Nations Conference on Environment and Development (UNCED) meeting in Rio de Janeiro in 1992 illustrated the enormous rift that has appeared between North and South. Not only is the agenda of the North different from that of the South, but the language, the discourse, is different. The paper, which was conceived as a contribution to the new discourse surrounding development and the environment explores the divergence between North and South in terms of the limited Northern perspective represented by ‘environmental managerialism’. The failure to grasp the global nature of environmental issues lies at the heart of the problem for radical scholarship. It is the central question to which, as sociologists, we should direct our energies.     

Within-Animal Variation as an Indication of the Minimal Magnitude of the Critical Effect Size for Continuous Toxicological Parameters Applicable in the Benchmark Dose Approach

In this study, the within-animal variation in routinely studied continuous toxicological parameters was estimated from temporal fluctuations in individual healthy nonexposed animals. Assuming that these fluctuations are nonadverse, this within-animal variation may be indicative of the minimal magnitude of the critical effect size (CES). The CES is defined as the breaking point between adverse and nonadverse changes in a continuous toxicological parameter, at the level of the individual organism. The total variation in the data from individual nonexposed animals was divided in variation parts due to known factors (differences in sex, animal, and day) and a residual variation, by means of analysis of variance. Using the residual variation and the estimated analytical measurement error of a toxicological parameter, the within-animal variation can be estimated. The data showed within-animal variations ranging between 0.6% and 34% for different clinical chemistry and hematological parameters in 90-day rat studies. This indicates that different (minimal) CES values may be applicable for different parameters.     

The effect of legalization and public funding of abortion on neonatal mortality: An intervention analysis

This paper examines the impact of the legalization of abortion on neonatal mortality in the United States. Monthly time series data are used to estimate intervention models separately for the U.S. as a whole and for the States of New York and South Carolina. Legalization of abortion in 1973 is found to have no discernible impact on national neonatal mortality rates. However, results from New York and South Carolina, states in which accessibility and public funding of abortion differed markedly, suggest that abortion is significantly related to declines in neonatal mortality, particularly among nonwhites. The magnitude and timing of such impacts varied between races and states.     

Unauthorized Mexican workers in the 1990 Los Angeles County labour force

By analysing how unauthorized Mexicans compare with seven other ethno'racial groups in Los Angeles County, separately and collectively, by educational attainment and time spent in the US, we find that unauthorized Mexicans had relatively fewer years of formal education (either in the US or in Mexico) and had been in the US a relatively fewer number of years than in-migrants of other ethno-racial backgrounds in 1990. These findings are then used as proxies to compare the human capital endowments of different ethno-racial groups. We next estimate the number of unauthorized Mexicans by occupation, industry and class of workers, and compare these distributions with the total labour force and with the other ethno-racial groups in Los Angeles County. To the extent that unauthorized Mexicans are found to be substitutes (complements) in the labour market, they can be expected to be a valid (invalid) empirical source of social tension and hence contemporary restrictionist immigration policy sentiment. Results show that amounts of human capital are positively related to the kinds of occupations filled. Analysis of the percentage of discordant pairs shows that unauthorized Mexicans are found to be most dissimilar (potential complements) to non-Latino (1) Anglos; (2) Blacks; (3) American Indians, Aleuts, and Eskimos; and (4) Asians and Pacific Islanders. Results also show that those ethno-racial groups most similar to (potential substitutes for) unauthorized Mexicans are (1) legal Mexican in-migrants and (2) other Latino foreign-born persons (both authorized and unauthorized). The ethno-racial group which falls into the intermediate realm of (dis)similarity is US-born Mexican. Consequently, for most persons residing in Los Angeles County the rise of restrictionist immigrant sentiment is not consistent with their labour market experiences, and restrictionist immigration policy, to the extent it is based on a labour market competition assumptions, may not be justified.     

A parametric model for heterogeneity in paired Poisson counts

We present a model for data in the form of matched pairs of counts. Our work is motivated by a problem in fission-track analysis, where the determination of a crystal's age is based on the ratio of counts of spontaneous and induced tracks. It is often reasonable to assume that the counts follow a Poisson distribution, but typically they are overdispersed and there exists a positive correlation between the numbers of spontaneous and induced tracks in the same crystal. We propose a model that allows for both overdispersion and correlation by assuming that the mean densities follow a bivariate Wishart distribution. Our model is quite general, having the usual negative-binomial and Poisson models as special cases. We propose a maximum-likelihood estimation method based on a stochastic implementation of the EM algorithm, and we derive the asymptotic standard errors of the parameter estimates. We illustrate the method with a data set of fission-track counts in matched areas of zircon crystals.     

Quelling Cabin Noise in Turboprop Aircraft via Active Control

Cabin noise in turboprop aircraft causes passenger discomfort, airframe fatigue, and employee scheduling constraints due to OSHA standards for exposure to high levels of noise. The noise levels in the cabins of turboprop aircraft are typically 10 to 30 decibels louder than commercial jet noise levels. However, unlike jet noise the turboprop noise spectrum is dominated by a few low frequency tones. Active structural acoustic control is a method in which the control inputs (used to reduce interior noise) are applied directly to a vibrating structural acoustic system. The control concept modeled in this work is the application of in-plane force inputs to piezoceramic patches bonded to the wall of a vibrating cylinder. The goal is to determine the force inputs and locations for the piezoceramic actuators so that (1) the interior noise is effectively damped; (2) the level of vibration of the cylinder shell is not increased; and (3) the power requirements needed to drive the actuators are not excessive. Computational experiments for data taken from a computer generated model and from a laboratory test article at NASA Langley Research Center are provided.