On calculating estimates of stratified error-components models

This note provides an AECM (alternating expectation conditional maximization) algorithm for calculating maximum-likelihood estimates of stratified error-components models. An advantage it has over other algorithms is that it can be easily modified to incorporate useful restrictions on the variance components. The new algorithm is applied in an example that illustrates the variance restrictions.

Some Monte Carlo results for a generalized error component model with heteroskedastic disturbances

This note provides Monte Carlo evidence illustrating that feasible and true GLS estimators of the Baltagi and Griffin (1988) generalized error component model do not have the same sampling behavior. Indeed, while the true GLS estimator is consistent, a feasible GLS estimator need not be, an observation corroborated by the Monte Carlo results.

Improving Supports for Youth of Color Traumatized by Violence

Many boys and young men of color live in communities where violence occurs too often and has a significant impact on their lives. This report examines the problem, offers strategies for various youth systems, and provides examples of approaches with strong outcomes for working with males of color who have witnessed or experienced violence

Payday loan pricing

We estimate the pricing determinants for 35,098 payday loans originated in Colorado between 2000 and 2006, and generate a number of results with implications for public policy. We find evidence consistent with classical price competition early in the sample, but as time passed these competitive effects faded and the data become more consistent with a variety of strategic pricing practices. On average, loan prices moved upward toward the legislated price ceiling over time, consistent with implicit collusion facilitated by price focal points. Large multi-store payday firms tended to charge higher prices than independent single-store operators, but were less likely to exploit inelastic demand near military bases and in largely minority neighborhoods. Of the three loan pricing measures used in our analysis, the annual percentage interest rate (APR) favored by regulators and analysts performed poorly.

Analyzing the Persistence of Referenced Web Resources with Memento

In this paper we present the results of a study into the persistence and availability of web resources referenced from papers in scholarly repositories. Two repositories with different characteristics, arXiv and the UNT digital library, are studied to determine if the nature of the repository, or of its content, has a bearing on the availability of the web resources cited by that content. Memento makes it possible to automate discovery of archived resources and to consider the time between the publication of the research and the archiving of the referenced URLs. This automation allows us to process more than 160000 URLs, the largest known such study, and the repository metadata allows consideration of the results by discipline. The results are startling: 45% (66096) of the URLs referenced from arXiv still exist, but are not preserved for future generations, and 28% of resources referenced by UNT papers have been lost. Moving forwards, we provide some initial recommendations, including that repositories should publish URL lists extracted from papers that could be used as seeds for web archiving systems.Comment: 4 pages, 5 figures. Accepted to Open Repositories 2011 Conferenc

Self-Selection and Tests for Bias and Risk in Mortgage Lending: Can You Price the Mortgage If You Don't Know the Process?

There is increasing interest in understanding the determinants of mortgage rejection by lenders and default by borrowers. Although many researchers have proposed simple single-equation models of rejection and default, we argue that far more complex econometric specifications are needed. This paper focuses attention on problems of sample selection in the process creating a sample of applicants for conventional mortgages. We illustrate that corrections for sample selection bias may have a substantial effect on estimation results and hence should not be ignored in studies of mortgage rejection or default.

Hot-spot tectonics of Eistla Regio, Venus: Results from Magellan images and Pioneer Venus gravity

Eistla Regio (ER) is a broad, low, discontinuous topographic rise striking roughly EW at low northern latitudes of Venus. Some 2000 x 7000 km in dimensions, it is the third largest rise in planform on Venus after Aphrodite Terra and Beta Phoebe Regiones. These rises are the key physiographic elements in a hot spot model of global tectonics including transient plume behavior. Since ER is the first such rise viewed by Magellan and the latitude is very favorable for Pioneer Venus gravity studies, some of the predictions of a time dependent hot spot model are tested. Western ER is defined as the rise including Gula and Sif Mons and central ER as that including Sappho Patera. Superior conjunction prevented Magellan from returning data on eastern ER (Pavlova) during the first mapping cycle. It is concluded that the western and central portions of ER, while part of the same broad topographic rise and tectonic framework, have distinctly different surface ages and gravity signatures. The western rise, including Gula and Sif Mons, is the expression of deep seated uplift with volcanism limited to the individual large shields. The eastern portion has been widely resurfaced more recently by thermal anomalies in the mantle

Targeting Intracellular Calcium Stores Alleviates Neurological Morbidities in a DFP-Based Rat Model of Gulf War Illness

Gulf War Illness (GWI) is a chronic multi-symptom disorder afflicting the veterans of the First Gulf War, and includes neurological symptoms characterized by depression and memory deficits. Chronic exposure to organophosphates (OP) is considered a leading cause for GWI, yet its pathobiology is not fully understood. We recently observed chronic elevations in neuronal Ca2+ levels ([Ca2+]i) in an OP- diisopropyl fluorophosphate (DFP) based rat model for GWI. This study was aimed at identifying mechanisms underlying elevated [Ca2+]i in this DFP model and investigating whether their therapeutic targeting could improve GWI-like neurological morbidities. Male Sprague-Dawley rats (9-wks) were exposed to DFP (0.5 mg/kg, s.c, 1x-daily for 5-d) and at 3-mos post DFP exposure, behavior was assessed and rats were euthanized for protein estimations and ratiometric Fura-2 [Ca2+]i estimations in acutely dissociated hippocampal neurons. In DFP rats, a sustained elevation in intracellular Ca2+ levels occurred, and pharmacological blockade of Ca2+-induced Ca2+-release mechanisms significantly lowered elevated [Ca2+]i in DFP neurons. Significant reductions in the protein levels of the ryanodine receptor (RyR) stabilizing protein Calstabin2 were also noted. Such a post-translational modification would render RyR leaky resulting in sustained DFP [Ca2+]i elevations. Antagonism of RyR with levetiracetam significantly lower elevated [Ca2+]i in DFP neurons and improved GWI-like behavioral symptoms. Since Ca2+ is a major second messenger molecule, such chronic increases in its levels could underlie pathological synaptic plasticity that expresses itself as GWI morbidities. Our studies show that treatment with drugs targeted at blocking intracellular Ca2+ release could be effective therapies for GWI neurological morbidities

Hidden Charge 2e Boson in Doped Mott Insulators: Field Theory of Mottness

We construct the low energy theory of a doped Mott insulator, such as the high-temperature superconductors, by explicitly integrating over the degrees of freedom far away from the chemical potential. For either hole or electron doping, a charge 2e bosonic field emerges at low energy. The charge 2e boson mediates dynamical spectral weight transfer across the Mott gap and creates a new charge e excitation by binding a hole. The result is a bifurcation of the electron dispersion below the chemical potential as observed recently in angle-resolved photoemission on Pb-doped Bi_2Sr_2CaCu_2O_{8+\delta} (Pb2212).Comment: 4 pages, 2 figures: Correct version to appear in PRL. Revisions include a derivation of the electron operator at low energies which reveals a branching structure seen recently in ARPES on Pb221