Estimation Methods for Duration Models

This paper is a selected overview of econometric methods for duration models and will appear in the forthcoming book The Economics of Search by the authors. The focus of the paper is on martingale methods for continuous time data and general methods for the analysis of discretetime data including multi-spell models and general life-history models.

THE GROCERY STORES' WAGE DISTRIBUTION: A SEMI-PARAMETRIC ANALYSIS OF THE ROLE OF RETAILING AND LABOR MARKET INSTITUTIONS

How and why has the wage distribution in U.S. grocery stores changed between 1984 and 1994? Unlike other industries in the time period, the important change in the wage distribution is not rising inequality, but the real wages fell across the entire wage distribution. Changes in labor market institutions explain more than half of the change in the wage distribution in grocery stores. Specifically, the decline in the real value of the minimum wage explains little of the decline in the mean real wage but much of the change in the shape of the distribution between 1984 and 1994, and 95 percent of the decline at the lowest 10th percentile. The decline in union coverage in grocery stores and the narrowing of the union-nonunion wage gap explains much of the decline above the 25th percentile. A third institutional change, the use of part-time employees, is not associated with the changes in grocery industry wage outcomes. One might think that the major changes in operation and technologies that occurred during this time period are at least contributing factors, but we find quite the contrary. If average store size, weekly operating hours, and the use of scanning technology had remained at their 1984 levels, the real wage decline would have been even greater than that actually seen, and for the entire wage distribution. Changes in grocery retailing prevented and even greater decline in real wages. Again unlike many other industries, skill-biased technological change does not appear important for grocery industry wage outcomes. The basis of our analysis is a statistical technique which combines nonparametric kernel density estimation with a parametric re-weighting, applied to Current Population Survey data supplemented with secondary data sources on the Grocery industry.Agribusiness, Labor and Human Capital,

Partial structure learning by subset Walsh transform.

Estimation of distribution algorithms (EDAs) use structure learning to build a statistical model of good solutions discovered so far, in an effort to discover better solutions. The non-zero coefficients of the Walsh transform produce a hypergraph representation of structure of a binary fitness function; however, computation of all Walsh coefficients requires exhaustive evaluation of the search space. In this paper, we propose a stochastic method of determining Walsh coefficients for hyperedges contained within the selected subset of the variables (complete local structure). This method also detects parts of hyperedges which cut the boundary of the selected variable set (partial structure), which may be used to incrementally build an approximation of the problem hypergraph

Workers' compensation claims related to natural rubber latex gloves among Oregon healthcare employees from 1987–1998

BACKGROUND: Occupational reaction to natural rubber latex (NRL) glove use by healthcare employees has been an area of increasing concern. Unfortunately, there is little data demonstrating the prevalence and severity of actual reactivity to NRL. METHOD: Occupational reaction to NRL was estimated using workers' compensation claims filed by healthcare employees in Oregon for the period of 1987–1998. For the first ten years, these claims were estimated by source and conditions consistent with NRL glove reactions, while in the last two years a specific code developed in 1997 for NRL glove reactions was also employed. RESULTS: The claim rate was on average 0.58 per 10,000 healthcare workers annually, which constituted 0.29% of all workers' compensation claims. The most common condition experienced was dermatitis (80%) and most common body part affected was the hands (55.4%). The majority of claimants, 45 (69.2%), reported taking less than a month off work, suggesting most reactions were minor in nature, although one fatality was reported. The average NRL claim cost was $8,309.48. Overall the average cost per insured healthcare worker was approximately$0.50 per year. The occupational groups with the highest number of claims were nurses (30.8% of claimants) and nursing aides and orderlies (24.6% of claimants). CONCLUSIONS: In comparison with other workers' compensation claims filed by healthcare workers during this period, 0.25% of the total was potentially related to NRL gloves. The rare incidence of respiratory and ocular claims is inconsistent with the hypothesis that asthmatic or conjunctival reactions to NRL gloves are common

An Investigation of Longwall Gob Gas Behavior and Control Methods

The National Institute for Occupational Safety and Health (NIOSH) has initiated the use of a tracer gas in field studies to characterize geologic and mining factors influencing the migration of longwall gob gas. Three studies have been conducted using sulfur hexafluoride (SF6) at a coal mine in the Northern Appalachian Basin operating in the Pittsburgh Coalbed. Eight underground tracer gas releases and one gob gas venthole release are summarized. The results indicate that the gas flow in the bleeder network and in the interior regions of longwall panel gobs do not strongly interact and that the negative pressure provided by gob gas venthole exhausters is very significant in maintaining this behavior. The data also show that ventilation practices employed in a large multi-panel gob area are functioning in accordance with the intent of the engineering design, a fact which would be difficult to evaluate using conventional mine ventilation measurement methods

Minimal walsh structure and ordinal linkage of monotonicity-invariant function classes on bit strings.

Problem structure, or linkage, refers to the interaction between variables in a black-box fitness function. Discovering structure is a feature of a range of algorithms, including estimation of distribution algorithms (EDAs) and perturbation methods (PMs). The complexity of structure has traditionally been used as a broad measure of problem difficulty, as the computational complexity relates directly to the complexity of structure. The EDA literature describes necessary and unnecessary interactions in terms of the relationship between problem structure and the structure of probabilistic graphical models discovered by the EDA. In this paper we introduce a classification of problems based on monotonicity invariance. We observe that the minimal problem structures for these classes often reveal that significant proportions of detected structures are unnecessary. We perform a complete classification of all functions on 3 bits. We consider nonmonotonicity linkage discovery using perturbation methods and derive a concept of directed ordinal linkage associated to optimization schedules. The resulting refined classification factored out by relabeling, shows a hierarchy of nine directed ordinal linkage classes for all 3-bit functions. We show that this classification allows precise analysis of computational complexity and parallelizability and conclude with a number of suggestions for future work

Universal subgap optical conductivity in quasi-one-dimensional Peierls systems

Quasi-one-dimensional Peierls systems with quantum and thermal lattice fluctuations can be modeled by a Dirac-type equation with a Gaussian-correlated off-diagonal disorder. A powerful new method gives the exact disorder-averaged Green function used to compute the optical conductivity. The strong subgap tail of the conductivity has a universal scaling form. The frequency and temperature dependence of the calculated spectrum agrees with experiments on KCP(Br) and trans-polyacetylene.Comment: 11 pages (+ 3 figures), LATEX (REVTEX 3.0

Pressure-Flow Characteristics of Normal and Disordered Esophageal Motor Patterns

Copyright © 2015 Elsevier Inc. All rights reserved This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Objective To perform pressure-flow analysis (PFA) in a cohort of pediatric patients who were referred for diagnostic manometric investigation. Study design PFA was performed using purpose designed Matlab-based software. The pressure-flow index (PFI), a composite measure of bolus pressurization relative to flow and the impedance ratio, a measure of the extent of bolus clearance failure were calculated. Results Tracings of 76 pediatric patients (32 males; 9.1 ± 0.7 years) and 25 healthy adult controls (7 males; 36.1 ± 2.2 years) were analyzed. Patients mostly had normal motility (50%) or a category 4 disorder and usually weak peristalsis (31.5%) according to the Chicago Classification. PFA of healthy controls defined reference ranges for PFI ≤142 and impedance ratio ≤0.49. Pediatric patients with pressure-flow (PF) characteristics within these limits had normal motility (62%), most patients with PF characteristics outside these limits also had an abnormal Chicago Classification (61%). Patients with high PFI and disordered motor patterns all had esophagogastric junction outflow obstruction. Conclusions Disordered PF characteristics are associated with disordered esophageal motor patterns. By defining the degree of over-pressurization and/or extent of clearance failure, PFA may be a useful adjunct to esophageal pressure topography-based classification