Heteroskedasticity-Robust Inference in Finite Samples

Since the advent of heteroskedasticity-robust standard errors, several papers have proposed adjustments to the original White formulation. We replicate earlier findings that each of these adjusted estimators performs quite poorly in finite samples. We propose a class of alternative heteroskedasticity-robust tests of linear hypotheses based on an Edgeworth expansions of the test statistic distribution. Our preferred test outperforms existing methods in both size and power for low, moderate, and severe levels of heteroskedasticity.

Modeling correlation in binary count data with application to fragile site identification

Available fragile site identification software packages (FSM and FSM3) assume that all chromosomal breaks occur independently. However, under a Mendelian model of inheritance, homozygosity at fragile loci implies pairwise correlation between homologous sites. We construct correlation models for chromosomal breakage data in situations where either partitioned break count totals (per-site single-break and doublebreak totals) are known or only overall break count totals are known. We derive a likelihood ratio test and NeymanâÂÂs C( ñ) test for correlation between homologs when partitioned break count totals are known and outline a likelihood ratio test for correlation using only break count totals. Our simulation studies indicate that the C( ñ) test using partitioned break count totals outperforms the other two tests for correlation in terms of both power and level. These studies further suggest that the power for detecting correlation is low when only break count totals are reported. Results of the C( ñ) test for correlation applied to chromosomal breakage data from 14 human subjects indicate that detection of correlation between homologous fragile sites is problematic due to sparseness of breakage data. Simulation studies of the FSM and FSM3 algorithms using parameter values typical for fragile site data demonstrate that neither algorithm is significantly affected by fragile site correlation. Comparison of simulated fragile site misclassification rates in the presence of zero-breakage data supports previous studies (Olmsted 1999) that suggested FSM has lower false-negative rates and FSM3 has lower false-positive rates

Heteroskedasticity-robust inference in finite samples

Since the advent of heteroskedasticity-robust standard errors, several papers have proposed adjustments to the original White formulation. We replicate earlier findings that each of these adjusted estimators performs quite poorly in finite samples. We propose a class of alternative heteroskedasticity-robust tests of linear hypotheses based on an Edgeworth expansion of the test statistic distribution. Our preferred test outperforms existing methods in both size and power for low, moderate, and severe levels of heteroskedasticity.National Science Foundation (U.S.). Graduate Research Fellowship (Grant 0645960

Nebraska’s Immigrant Population: Economic and Fiscal Impacts - OLLAS Report No. 5

Immigration issues have once again assumed center stage in policy circles at every level of government in the United States, as the number of new immigrants, many undocumented and many from Latin American nations, has risen markedly in recent years. This is certainly true in Nebraska. According to US Census figures for 2000, the total immigrant population in Nebraska was estimated to be 74,638. By 2006, this figure had risen to 99,500, a 33.3 percent increase. By comparison, the total native-born population in the state grew less than 2.0 percent over the same six-year period. This study attempts to quantitatively measure the impact of the state’s immigrant population on the Nebraska economy, with some attention paid to Latin American immigrant groups

The Economic Impact of Latin American & Other Immigrants Iowa, Nebraska and the Omaha-Council Bluffs Metropolitan Area

Although recent research from the Pew Hispanic Center suggests that the rate of recent immigration to the United States has slowed considerably, other studies clearly show that immigrants make substantial economic contributions to the communities in which they settle. This report focuses attention on the quantitative economic impact of first-generation, foreign-born individuals on the Omaha-Council Bluffs economy as well as the Nebraska and Iowa state economies in 2010

Seal for a rotating member

A face seal assembly is provided having an annular seal body mounted in an axially moveable relationship to a seal support structure. A piston ring is disposed between the annular seal body and the seal support structure forming a secondary seal. A first locator spring, which is an annular wave spring, is disposed between said seal support structure and the piston ring to urge the piston ring in an axial direction. Optionally, a second locator spring, also a wave spring, may be disposed between the piston ring and the seal support structure for urging the piston ring in a radial direction

Ecotypic Differentiation of Mid-Atlantic \u3ci\u3eQuercus\u3c/i\u3e Species in Response to Ultramafic Soils

Spatial heterogeneity of soil conditions combined with intraspecific variation confer site-specific edaphic tolerance, resulting in local adaptation and speciation. To understand the geoecological processes controlling community assembly of woodland tree species on serpentine and mafic soils, we investigated resource gradients and provenance (geographic area of propagule collection) as variables affecting typical representative upland oak (Quercus) species distribution. Accordingly, we conducted a year-long reciprocal transplant experiment in the greenhouse with serpentine and mafic soils, using seedlings of five oak species (Quercus marilandica, Q. stellata, Q. montana, Q. michauxii and Q. alba). All seedlings, regardless of provenance or soil depth, displayed more robust growth in the mafic soils. Soil depth was an important determinant, with all species exhibiting increased growth in the deeper-soil treatments. Fitness surrogates such as stem height, relative growth rate, and leaves per plant were greater when seedlings were grown in their home soil than when they were grown in the non-resident soil, suggesting an ecotypic effect. Mean stomatal conductance and stem growth were positively correlated with soil depth in all treatments. Taken together, the study showed provenance-specific growth responses of oak seedlings to soil type and depth, providing a better understanding of the mechanisms controlling species assembly in woodland communities

Metaheuristic Design Patterns: New Perspectives for Larger-Scale Search Architectures

Design patterns capture the essentials of recurring best practice in an abstract form. Their merits are well established in domains as diverse as architecture and software development. They offer significant benefits, not least a common conceptual vocabulary for designers, enabling greater communication of high-level concerns and increased software reuse. Inspired by the success of software design patterns, this chapter seeks to promote the merits of a pattern-based method to the development of metaheuristic search software components. To achieve this, a catalog of patterns is presented, organized into the families of structural, behavioral, methodological and component-based patterns. As an alternative to the increasing specialization associated with individual metaheuristic search components, the authors encourage computer scientists to embrace the ‘cross cutting' benefits of a pattern-based perspective to optimization algorithms. Some ways in which the patterns might form the basis of further larger-scale metaheuristic component design automation are also discussed