Página 1 dos resultados de 900 itens digitais encontrados em 0.011 segundos

## Unobserved Worker Ability, Firm Heterogeneity, and the Returns to Schooling and Training

Lopes, Ana Sofia; Teixeira, Paulino
Fonte: FEUC. Grupo de Estudos Monetários e Financeiros Publicador: FEUC. Grupo de Estudos Monetários e Financeiros
Tipo: Trabalho em Andamento
ENG
Relevância na Pesquisa
36.990012%
It is well known that unobserved heterogeneity across workers and firms seriously impacts the computation of the determinants of individual earnings in standard human capital earnings functions. Following the tradition of AKM (Abowd, Kramarz, and Margolis, 1999), this paper offers an alternative way of controlling unknown worker and firm heterogeneity by taking full advantage of a matched employee-employer dataset based on two key Portuguese micro databases. Our modelling strategy assumes that the gap between individual and firm average wages, unexplained by differences in observable characteristics, gives the extent to which the unobserved ability of a given individual deviates from the unobserved worker average ability in the firm. This methodology has, in particular, the advantage of not relying exclusively on information on job switchers to identify worker and firm effects, thus avoiding any bias arising from endogenous worker mobility. Another important aspect of our treatment is that it allows the estimation of worker effects without risk of contamination from firm effects. To test our modelling we use an original 2-year longitudinal LEED dataset, comprising of more than 400 thousand workers and 1,500 firms in each year. We focus on two separate sets of individuals (i.e. stayers and switchers) and provide a variety of robustness tests...

## Por dentro da quebrada: a heterogeneidade social de Ermelino Matarazzo e da periferia; Inside the hood: the social heterogeneity of Ermelino Matarazzo and the periphery.

Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Relevância na Pesquisa
36.891902%
Esta pesquisa analisou um distrito periférico da Zona Leste de São Paulo: Ermelino Matarazzo. A abordagem microssocial permitiu relacionar vários fenômenos que caracterizaram a periferização da cidade de São Paulo como a industrialização, imigração, migração, loteamento, autoconstrução, formação de favelas e como tais fenômenos incidiram na segregação social na periferia a partir de um distrito. Discutiu-se o valor simbólico da periferia leste e a hierarquização dos espaços, à luz da formação dos agentes ali inseridos para discutir a heterogeneidade social local. Comprovou-se a hipótese da diferenciação interna de Ermelino Matarazzo a partir de três processos distintos pelo qual o distrito passou a partir da instalação da primeira indústria na década de 1940. Foram propostas três regiões: a dos loteamentos que foi caracterizada pela urbanização a partir de loteamentos/autoconstrução até a década de 1970; a região das ocupações que foi formada pelo surgimento de favelas a partir da década de 1970; e, por fim, a região das construtoras que constituiu uma região por empreendimentos imobiliários que venderam casas construídas a partir de 1980. Um dos resultados desta heterogeneidade social pôde ser percebido pela forma como foram distribuídas espacialmente em Ermelino Matarazzo as escolas públicas e privadas...

## Estudo dos efeitos de escala em ensaios de penetração dinâmica; Study of scale effects in dynamic penetration tests

Dalla Rosa, Salete
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
36.905383%

## Numerical Characterization of Concrete Heterogeneity

Pitangueira,Roque Luiz; Silva,Raul Rosas e
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
37.056475%
In this paper, a finite element model including both material heterogeneity and size effects is presented. The concrete is considered as a statistical combination of constituent phase with different properties (aggregate, mortar and interface material). The material point response is based on a combination of the random occurrence of the solid phases in the structural volume as well as on the differences of structural response due to the size effect. Such combination allows for higher or lower heterogeneity corresponding to smaller or larger structural size. Simulations of the material heterogeneity and associated size effect in a computationally efficient and simple manner show good qualitative agreement with available experimental results for the three-point bending and Brazilian split tests.

## Extending nondirectional heterogeneity tests to evaluate simply ordered alternative hypotheses.

Rice, W R; Gaines, S D
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.12308%
Biologists frequently use nondirectional heterogeneity tests when comparing three or more populations because a suitable directional test is unavailable or is not practical to implement. Here we describe a test, the ordered heterogeneity test, that permits testing against simply ordered alternative hypotheses in the context of almost any nondirectional test. The test has a wide range of parametric and nonparametric applications. Graphs are developed for calculating exact P values.

## The search for heterogeneity in insulin-dependent diabetes mellitus (IDDM): linkage studies, two-locus models, and genetic heterogeneity.

Hodge, S E; Anderson, C E; Neiswanger, K; Sparkes, R S; Rimoin, D L
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.104473%
One hundred families with insulin-dependent diabetes mellitus (IDDM) were analyzed for linkage with 27 genetic markers, including HLA, properdin factor B (BF), and glyoxalase 1(GLO) on chromosome 6, and Kidd blood group (Jk) on chromosome 2. The linkage analyses were performed under several different genetic models. An approximate correction for two-locus linkage analysis was developed and applied to four markers. Two different heterogeneity tests were implemented and applied to all the markers. One, the Predivided-Sample Test, utilizes various criteria thought to be relevant to genetic heterogeneity in IDDM. The other, the Admixture Test, looks for heterogeneity without specifying a prior how the sample should be divided. Results continued to support linkage of IDDM with three chromosome 6 markers: HLA, BF, and GLO. The total lod score for Kidd blood group, under the recessive model with 20% penetrance, is 1.63--down 1.2 from the 2.83 reported by us earlier. The only other marker whose lod score exceeded 1.0 under any model was pancreatic amylase (AMY2). The two-locus correction, which involved lowering the penetrance values used in the analysis, affected estimates of theta (recombination fraction) but did not markedly change the lod scores themselves. There was little evidence for heterogeneity within any of the lod scores...

## Age and sex based genetic locus heterogeneity in type 1 diabetes

Paterson, A.; Petronis, A.
Fonte: BMJ Group Publicador: BMJ Group
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.056475%
BACKGROUND—Two genome scans for susceptibility loci for type 1 diabetes using large collections of families have recently been reported. Apart from strong linkage in both studies of the HLA region on chromosome 6p, clear consistent evidence for linkage was not observed at any other loci. One possible explanation for this is a high degree of locus heterogeneity in type 1 diabetes, and we hypothesised that the sex of affected offspring, age of diagnosis, and parental origin of shared alleles may be the bases of heterogeneity at some loci. METHODS—Using data from a genome wide linkage study of 356 affected sib pairs with type 1 diabetes, we performed linkage analyses using parental origin of shared alleles in subgroups based on (1) sex of affected sibs and (2) age of diagnosis. RESULTS—Among the results obtained, we observed that evidence for linkage to IDDM4 on chromosome 11q13 occurred predominantly from opposite sex, rather than same sex sib pairs. At a locus on chromosome 4q, evidence for linkage was observed in sibs where one was diagnosed above the age of 10 years and the other diagnosed below 10 years of age. CONCLUSIONS—We show that heterogeneity tests based on age of diagnosis, sex of affected subject, and parental origin of shared alleles may be helpful in reducing locus heterogeneity in type 1 diabetes. If repeated in other samples...

## A combined test of linkage heterogeneity.

Goldstein, D. R.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.371943%
This paper focuses on the problem of testing for heterogeneity once linkage is established. In an investigation of genetic linkage, Morton first proposed a general purpose test to detect heterogeneity in the recombination fraction. Two more commonly used tests of linkage heterogeneity are the admixture test (A-test) of Smith, Ott, and Risch and Baron, and the B-test of Risch. All are likelihood-ratio tests, but they differ in the models specifying the heterogeneity. A new test of heterogeneity in the presence of linkage is presented here. I propose a mixture model of heterogeneity, which allows the recombination fraction to vary among families, as does the B-model, yet also allows some families to be unlinked, as the A-model does. This model contains the A and B models as special cases and thus allows a direct test (D-test), which can provide justification for choosing one of these extremes.

## Tumor Heterogeneity: Mechanisms and Bases for a Reliable Application of Molecular Marker Design

Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.371943%
Tumor heterogeneity is a confusing finding in the assessment of neoplasms, potentially resulting in inaccurate diagnostic, prognostic and predictive tests. This tumor heterogeneity is not always a random and unpredictable phenomenon, whose knowledge helps designing better tests. The biologic reasons for this intratumoral heterogeneity would then be important to understand both the natural history of neoplasms and the selection of test samples for reliable analysis. The main factors contributing to intratumoral heterogeneity inducing gene abnormalities or modifying its expression include: the gradient ischemic level within neoplasms, the action of tumor microenvironment (bidirectional interaction between tumor cells and stroma), mechanisms of intercellular transference of genetic information (exosomes), and differential mechanisms of sequence-independent modifications of genetic material and proteins. The intratumoral heterogeneity is at the origin of tumor progression and it is also the byproduct of the selection process during progression. Any analysis of heterogeneity mechanisms must be integrated within the process of segregation of genetic changes in tumor cells during the clonal expansion and progression of neoplasms. The evaluation of these mechanisms must also consider the redundancy and pleiotropism of molecular pathways...

## Binomial Mixture Model-based Association Tests under Genetic Heterogeneity

Zhou, Hui; Pan, Wei
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.416802%
Most of the existing association tests for population-based case-control studies are based on comparing the mean genotype scores between the case and control groups, which may not be efficient under genetic heterogeneity. Given that most common diseases are genetically heterogeneous, caused by mutations in multiple loci, it may be beneficial to fully account for genetic heterogeneity in an association test. Here we first propose a binomial mixture model for such a purpose and develop a corresponding mixture likelihood ratio test (MLRT) for a single locus. We also consider two methods to combine single-locus-based MLRTs across multiple loci in linkage disequilibrium to boost power when causal SNPs are not genotyped. We show with a wide spectrum of numerical examples that under genetic heterogeneity the proposed tests are more powerful than some commonly used association tests.

## An evaluation of different meta-analysis approaches in the presence of allelic heterogeneity

Asimit, Jennifer; Day-Williams, Aaron; Zgaga, Lina; Rudan, Igor; Boraska, Vesna; Zeggini, Eleftheria
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.287651%
Meta-analysis has proven a useful tool in genetic association studies. Allelic heterogeneity can arise from ethnic background differences across populations being meta-analyzed (for example, in search of common frequency variants through genome-wide association studies), and through the presence of multiple low frequency and rare associated variants in the same functional unit of interest (for example, within a gene or a regulatory region). The latter challenge will be increasingly relevant in whole-genome and whole-exome sequencing studies investigating association with complex traits. Here, we evaluate the performance of different approaches to meta-analysis in the presence of allelic heterogeneity. We simulate allelic heterogeneity scenarios in three populations and examine the performance of current approaches to the analysis of these data. We show that current approaches can detect only a small fraction of common frequency causal variants. We also find that for low-frequency variants with large effects (odds ratios 2–3), single-point tests have high power, but also high false-positive rates. P-value based meta-analysis of summary results from allele-matching locus-wide tests outperforms collapsing approaches. We conclude that current strategies for the combination of genetic association data in the presence of allelic heterogeneity are insufficiently powered.

## A likelihood ratio test for genomewide association under genetic heterogeneity*

Qian, Meng; Shao, Yongzhao
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.287651%
Most existing association tests for genome-wide association studies (GWAS) fail to account for genetic heterogeneity. Zhou and Pan proposed a binomial mixture model based association test to account for the possible genetic heterogeneity in case-control studies. The idea is elegant, however, the proposed test requires an EM-type iterative algorithm to identify the penalized maximum likelihood estimates and a permutation method to assess p-values. The intensive computational burden induced by the EM-algorithm and the permutation becomes prohibitive for direct applications to genome-wide association studies. This paper develops a likelihood ratio test (LRT) for genome-wide association studies under genetic heterogeneity based on a more general alternative mixture model. In particular, a closed-form formula for the likelihood ratio test statistic is derived to avoid the EM-type iterative numerical evaluation. Moreover, an explicit asymptotic null distribution is also obtained which avoids using the permutation to obtain p-values. Thus, the proposed LRT is easy to implement for genome-wide association studies (GWAS). Furthermore, numerical studies demonstrate that the LRT has power advantages over the commonly used Armitage trend test and other existing association tests under genetic heterogeneity. A breast cancer GWAS data set is used to illustrate the newly proposed LRT.

## Heterogeneity of Leishmania donovani Parasites Complicates Diagnosis of Visceral Leishmaniasis: Comparison of Different Serological Tests in Three Endemic Regions

Abass, Elfadil; Kang, Cholho; Martinkovic, Franjo; Semião-Santos, Saul J.; Sundar, Shyam; Walden, Peter; Piarroux, Renaud; el Harith, Abdallah; Lohoff, Michael; Steinhoff, Ulrich
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.312688%
Diagnostic tests for visceral leishmaniasis that are based on antigens of a single Leishmania strain can have low diagnostic performance in regions where heterologous parasites predominate. The aim of this study was to investigate and compare the performance of five serological tests, based on different Leishmania antigens, in three endemic countries for visceral leishmaniasis. A total number of 231 sera of symptomatic and asymptomatic cases and controls from three endemic regions of visceral leishmaniasis in East Sudan, North India and South France were evaluated by following serological tests: rKLO8- and rK39 ELISA, DAT (ITMA-DAT) and two rapid tests of rK39 (IT LEISH) and rKE16 (Signal-KA). Overall, rKLO8- and rK39 ELISA were most sensitive in immunocompetent patients from all endemic regions (96–100%) and the sensitivity was reduced to 81.8% in HIV co-infected patients from France. Sera of patients from India demonstrated significantly higher antibody responses to rKLO8 and rK39 compared with sera from Sudan (p<0.0001) and France (p<0.0037). Further, some Indian and Sudanese patients reacted better with rKLO8 than rK39. Sensitivity of DAT (ITMA-DAT) was high in Sudan (94%) and India (92.3%) but low in France being 88.5% and 54.5% for VL and VL/HIV patients...

## Nonparametric Tests for Treatment Effect Heterogeneity

Mitnik, Oscar K.; Imbens, Guido; Hotz, V. Joseph; Crump, Richard K.
EN_US
Relevância na Pesquisa
27.318694%
In this paper we develop two nonparametric tests of treatment effect heterogeneity. The first test is for the null hypothesis that the treatment has a zero average effect for all subpopulations defined by covariates. The second test is for the null hypothesis that the average effect conditional on the covariates is identical for all subpopulations, that is, that there is no heterogeneity in average treatment effects by covariates. We derive tests that are straightforward to implement and illustrate the use of these tests on data from two sets of experimental evaluations of the effects of welfare-to-work programs.; Economics

## Effects of Heterogeneous Parameter Distributions on Hydraulic Tests : Analysis and Assessment; Wirkung heterogener Parameterverteilungen auf hydraulische Tests : Analyse und Bewertung

Leven, Carsten
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
37.87758%
Groundwater flow and transport processes are dominated by the heterogeneity of the subsurface. In the last decades, the importance of a detailed description, characterization, and quantification of aquifer heterogeneity became more and more evident. The present work is motivated by the requirement of an improved understanding of the interrelationship of effects resulting from heterogeneity on particular measurements, and by the importance of a detailed characterization of heterogeneity. To account for these issues, two different approaches are applied: 1) Experimental tests conducted to a fractured sandstone block allowing the practical investigation of effects arising from the strongly heterogeneous nature of the sample. 2) A theoretical approach based on the analysis of sensitivity coefficients enabling the improvement of the theoretical comprehension of effects arising from aquifer heterogeneity. The experimental investigation of the fractured porous rock shows effects arising from the heterogeneity of the fractured system. However, the comparison of the experimental results exemplifies the necessity of an improved understanding of the interrelation between an arbitrary parameter distribution and the response of a particular hydraulic measurement. A promising concept to account for this interrelationship is the Sensitivity Coefficient Approach (SCA). The SCA is applied to investigate the intrinsic characteristics of hydraulic tests giving a better understanding of the response of hydraulic tests due to aquifer heterogeneity. As the approach allows the assessment of information from distinct time periods during a hydraulic test...

## Functional Literacy, Heterogeneity and the Returns to Schooling : Multi-Country Evidence

Fasih, Tazeen; Patrinos, Harry Anthony; Sakellariou, Chris
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
Tipo: Publications & Research :: Policy Research Working Paper; Publications & Research
ENGLISH; EN_US
Relevância na Pesquisa
37.159265%

## Organically Modified Mesoporous Silica as a Support for Synthesis and Catalysis

McEleney, Kevin
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 14165145 bytes; application/pdf
EN; EN
Relevância na Pesquisa
36.65929%
Mesoporous silicates are excellent materials for supported catalysis due to their ease of functionalization, tunable pore size and high surface areas. Mesoporous silicates have been utilized in a variety of applications such as drug delivery scaffolds and catalyst supports. Functionalization of the surface can be achieved by either grafting of alkoxy silanes or co-condensation of the organosilane with the inorganic silica source. My research in this area can be divided into two components. In the first, we address the significant issue of metal contamination after reactions that are catalyzed by transition metals. In the second, we examine the design of new catalysts based on organic/inorganic composites. Ruthenium catalyzed processes such as olefin metathesis or asymmetric hydrogenation, are often underutilized due to the difficulty of removing the ruthenium by-products. Attempts to remove ruthenium involve treating the solution with a scavenging reagent followed by silica chromatography. Often these scavenging agents are expensive phosphines or toxic agents like lead tetra-acetate. SBA-15 functionalized with aminopropyl triethoxysilane displays a high affinity for ruthenium. Furthermore, it can be utilized to remove ruthenium by-products from olefin metathesis or hydrogenation reactions without the need for silica chromatography. We have also prepared sulfur-functionalized mesoporous silicates that have a high affinity for palladium. The materials after loading prove to be active catalysts for a variety of palladium catalyzed processes such as Suzuki-Miyaura and Sonogashira couplings. The catalysts are recyclable with moderate loss of activity and structure...

## Neyman's C(\alpha) Test for Unobserved Heterogeneity

Gu, Jiaying
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.567559%
A unified framework is proposed for tests of unobserved heterogeneity in parametric statistic models based on Neyman's $C(\alpha)$ approach. Such tests are irregular in the sense that the first order derivative of the log likelihood with respect to the heterogeneity parameter is identically zero, and consequently the conventional Fisher information about the parameter is zero. Nevertheless, local asymptotic optimality of the $C(\alpha)$ tests can be established via LeCam's differentiability in quadratic mean and the limit experiment approach. This leads to local alternatives of order $n^{-1/4}$. The scalar case result is already familiar from existing literature and we extend it to the multi-dimensional case. The new framework reveals that certain regularity conditions commonly employed in earlier developments are unnecessary, i.e. the symmetry or third moment condition imposed on the heterogeneity distribution. Additionally, the limit experiment for the multi-dimensional case suggests modifications on existing tests for slope heterogeneity in cross sectional and panel data models that lead to power improvement. Since the $C(\alpha)$ framework is not restricted to the parametric model and the test statistics do not depend on the particular choice of the heterogeneity distribution...

## Survey Expectations

Pesaran, M. Hashem; Weale, Martin
Formato: 478132 bytes; application/pdf; application/pdf
EN_GB
Relevância na Pesquisa
36.732473%
This paper focuses on survey expectations and discusses their uses for testing and modeling of expectations.Alternative models of expectations formation are reviewed and the importance of allowing for heterogeneity of expectations is emphasized. A weak form of the rational expectations hypothesis which focuses on average expectationsrather than individual expectations is advanced. Other models of expectations formation, such as the adaptive expectations hypothesis, are briefly discussed. Testable implications of rational and extrapolative models of expectationsare reviewed and the importance of the loss function for the interpretation of the test results is discussed. The paper thenprovides an account of the various surveys of expectations, reviews alternative methods of quantifying the qualitative surveys, and discusses the use of aggregate and individual survey responses in the analysis of expectations and for forecasting.

## Nonparametric Tests for Treatment Effect Heterogeneity

Hotz, V.J.; Crump, Richard; Imbens, Guido; Mitnik, Oscar
Fonte: Review of Economics and Statistics Publicador: Review of Economics and Statistics
Tipo: Artigo de Revista Científica Formato: 233881 bytes; application/pdf