Normalization in Econometrics

The issue of normalization arises whenever two different values for a vector of unknown parameters imply the identical economic model. A normalization implies not just a rule for selecting which among equivalent points to call the maximum likelihood estimate (MLE), but also governs the topography of the set of points that go into a small-sample confidence interval associated with that MLE. A poor normalization can lead to multimodal distributions, disjoint confidence intervals, and very misleading characterizations of the true statistical uncertainty. This paper introduces an identification principle as a framework upon which a normalization should be imposed, according to which the boundaries of the allowable parameter space should correspond to loci along which the model is locally unidentified. We illustrate these issues with examples taken from mixture models, structural vector autoregressions, and cointegration models.     

Cocoa Pod Borer (Conopomorpha cramerella Snellen) in Papua New Guinea: Biosecurity Models for New Ireland and the Autonomous Region of Bougainville

Cocoa Pod Borer (Conopomorpha cramerella Snellen) (CPB) is an important pest of cocoa. Following its emergence as a pest in East New Britain, Papua New Guinea, in 2006, it was considered relevant to assess its potential spread to other cocoa growing regions. Its likelihood of introduction to the islands of Bougainville and New Ireland from East New Britain Province, Papua New Guinea, was modeled using Monte Carlo simulation. This dispersal model was based around different scenarios, identifying trends rather than explicitly attempting to encapsulate true values. The model suggested that CPB is far more likely to establish on New Ireland than on Bougainville. More important, incertitude resulting from incomplete knowledge of the amount and frequency of cocoa transported between islands had a significant effect on model outputs. Quarantine and agriculture officials will be able to refine these parameter values, and then use the relevant scenarios from those presented here as a guide to develop quarantine procedures. In addition, a contingency model was employed to estimate the optimal sampling effort to use following an incursion of CPB into Bougainville or New Ireland and the seemingly successful implementation of an initial eradication program. The model suggests that at a 1% infestation level, sampling should continue for 2.5–2.7 years (90% CI) after claiming eradication, and this estimate changed little for higher infestation levels. Through modeling variations in sampling intensity, the model also suggested that determining the full spread of CPB is more important than increased sampling within one region.     

Book review

State-Space Models with Regime Switching by Chang-Jin Kim and Charles R. Nelson. Pp. 250. Cambridge, Massachnsetts: MIT Press, 1999. ($40.00 cloth) WEB INFOR~UATION: http://mitpress.mit.edu/book-home.tcl?isbn=0262l123.     

Model validation: an annotated bibliography

This paper contains an annotated bibliography of 316 papers and books relevant to model validation, with emphasis on articles of potential interest to statisticians. The bibliography is accompanied by a brief introduction, a list of some important areas for statistical research, a short glossary, and a key word index.     

Combining non-linear regressions that have unequal error variances and some parameters in common

Methods of estimation and inference are presented for the situation where two non-linear regression models with unequal error variances contain some parameters in common. Such a situation arises in structural chemistry, when bond lengths are available for three nearly collinear atoms in crystals and a model is required to quantify the extent and form of the relationship between the longer and the shorter bond. Some atomic triples are symmetric and require a different model and error variance from those required by the asymmetric triples. The profile likelihood for the regression parameters is a weighted sum of the logarithms of the sums-of-squares functions from each model, and the estimates can be obtained by using a simple modification to a standard non-linear least squares program. A likelihood ratio test for assessing whether the parameters in common are equal is described. When these techniques are applied to two data sets consisting of bond lengths for bromine–tellurium–bromine and sulphur–tellurium–sulphur triples, there is no evidence against the equality hypothesis. An extension to the model to allow for a non-constant variance is required for proper analysis of the sulphur–tellurium–sulphur data.     

Retracted Article: Growth attenuation and young people with profound disabilities – why we need to talk about Charley

In 2004 an intervention known as the Ashley Treatment (AT) was sought on behalf of Ashley X, a girl with severe developmental disabilities. A discursive interpretive framework is used to investigate use of the AT in the case of Charley Hooper in New Zealand in 2009. This investigation found that use of the AT is intimately bound up in ideas about worthiness of life related to the ability to act as an autonomous agent within social structures. Questions this case raises about ethical decision-making and future physical and social requirements for profoundly disabled young people in the future are posed.     

Inequality in the “Cradle of Liberty”: Race/Ethnicity and Wealth in Greater Boston

New data collected for the Boston Metropolitan Statistical Area provide detailed information on financial assets that allow analysis to extend beyond the traditional black–white divide. Targeting US-born blacks, Caribbean blacks, Puerto Ricans, Dominicans, and other Hispanics, findings from the National Asset Scorecard for Communities of Color survey underscore the large racial and ethnic disparities in financial wealth, even after controlling for demographic and socioeconomic status. Further, some notable differences between Boston’s communities of color highlight the importance of detailed analyses for research on the racial wealth gap. In particular, among non-white communities Dominicans report comparatively low asset and high debt amounts, while Caribbean blacks report relatively higher levels of wealth. Altogether, these findings point to the need for wealth building opportunities in communities of color and further investigation of the causes and consequences of financial disparities between groups of color disaggregated by specific ancestral origin.     

Work status, benefits, and financial resources among people with HIV/AIDS

With the advent of more advanced treatments and therapies, people with HIV/AIDS are experiencing significant improvements in their health, making many of their ongoing employment and career goals more realistic. However, people with HIV/AIDS continue to have major concerns regarding the impact of working on their benefits and entitlements, including apprehensions about potential economic hardships related to loss of financial supports and health insurance coverage. This article focuses on factors related to employment status, sources of health benefits, and entitlements among people with HIV/AIDS. In addition, results of the study demonstrate differences in employment status, benefit types, and the amount of financial support individuals receive based on gender.