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## ‣ Evidence on Gender Wage Discrimination in Portugal: parametric and semi-parametric approaches

Galego, Aurora; Pereira, João
Tipo: Trabalho em Andamento
Português
Relevância na Pesquisa
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In this paper we use two alternative approaches to study the extent of gender wage discrimination in Portugal. Both methods involve the estimation of wage equations for males and females and the Blinder [1973] and Oaxaca [1973] decomposition. However, to take into account possible sample selection bias, we consider both parametric and semi-parametric methods. First, we consider a parametric approach that relies on distributional assumptions about the distribution of the error terms in the model (Vella (1992, 1998) and Wooldridge (1998)). Within this approach, if the distributional assumption is not satisfied, the parameters’ estimates may be inconsistent. Secondly, we apply Li and Wooldridge [2002] semi-parametric estimator, which does not assume any known distribution on the joint distribution of the errors of the wage equation and of the sample selection equation; the distribution has an unknown form and is estimated through non-parametric kernel techniques.We employ micro data for Portugal from the European Community Household Panel (ECHP). The results from both approaches provide evidence in favour of the existence of gender wage discrimination in Portugal. However, the extent of labour market discrimination decreases when sample selection bias corrections are taken into account.

## ‣ Estimating the Parameters of Selection on Nonsynonymous Mutations in Drosophila pseudoobscura and D. miranda

Haddrill, Penelope R.; Loewe, Laurence; Charlesworth, Brian
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.7346%
We present the results of surveys of diversity in sets of >40 X-linked and autosomal loci in samples from natural populations of Drosophila miranda and D. pseudoobscura, together with their sequence divergence from D. affinis. Mean silent site diversity in D. miranda is approximately one-quarter of that in D. pseudoobscura; mean X-linked silent diversity is about three-quarters of that for the autosomes in both species. Estimates of the distribution of selection coefficients against heterozygous, deleterious nonsynonymous mutations from two different methods suggest a wide distribution, with coefficients of variation greater than one, and with the average segregating amino acid mutation being subject to only very weak selection. Only a small fraction of new amino acid mutations behave as effectively neutral, however. A large fraction of amino acid differences between D. pseudoobscura and D. affinis appear to have been fixed by positive natural selection, using three different methods of estimation; estimates between D. miranda and D. affinis are more equivocal. Sources of bias in the estimates, especially those arising from selection on synonymous mutations and from the choice of genes, are discussed and corrections for these applied. Overall...

## ‣ Validation, Replication, and Sensitivity Testing of Heckman-Type Selection Models to Adjust Estimates of HIV Prevalence

Clark, Samuel J.; Houle, Brian
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.667798%
A recent study using Heckman-type selection models to adjust for non-response in the Zambia 2007 Demographic and Health Survey (DHS) found a large correction in HIV prevalence for males. We aim to validate this finding, replicate the adjustment approach in other DHSs, apply the adjustment approach in an external empirical context, and assess the robustness of the technique to different adjustment approaches. We used 6 DHSs, and an HIV prevalence study from rural South Africa to validate and replicate the adjustment approach. We also developed an alternative, systematic model of selection processes and applied it to all surveys. We decomposed corrections from both approaches into rate change and age-structure change components. We are able to reproduce the adjustment approach for the 2007 Zambia DHS and derive results comparable with the original findings. We are able to replicate applying the approach in several other DHSs. The approach also yields reasonable adjustments for a survey in rural South Africa. The technique is relatively robust to how the adjustment approach is specified. The Heckman selection model is a useful tool for assessing the possibility and extent of selection bias in HIV prevalence estimates from sample surveys.

## ‣ Are Foreign Migrants More Assimilated Than Native Ones?

FAINI, Riccardo; STRØM, Steinar; VENTURINI, Alessandra; VILLOSIO, Claudia
Fonte: Instituto Universitário Europeu Publicador: Instituto Universitário Europeu
Tipo: Trabalho em Andamento
Português
Relevância na Pesquisa
18.187598%
The novelties of the paper are two. First the paper compares the pattern of wage assimilation of foreigners with both native immigrants and local natives in Italy, a country with large internal and international migration. This comparison demonstrates the role played by language and knowledge of social capital in the assimilation of immigrants relative to both natives and internal immigrants. Second we model new corrections of the selection bias due to return migration. In the wage equation we correct for selection bias through a duration extension of the traditional Heckman correction term and alternatively we use a hazard rate correction. The empirical test use the Italian administrative dataset on dependent employment (WHIP), to estimate a fixed effect model of the weekly wages of males aged 18-45 with controls for selection in return migration and unobserved heterogeneity. The three groups of workers start their careers at the same wage level but, as experience increases, the wage profiles of foreigners and natives, both immigrants and locals, diverge. A positive selection in the returns prevails, with both corrections, so that the foreign workers with lower wages are the most likely to stay in Italy. Also an “ethnic” skill differential emerges.

## ‣ Wage assimilation : migrants versus natives and foreign migrants versus internal migrants

STRØM, Steinar; VENTURINI, Alessandra; VILLOSIO, Claudia
Fonte: Instituto Universitário Europeu Publicador: Instituto Universitário Europeu
Tipo: Trabalho em Andamento Formato: application/pdf; digital
Português
Relevância na Pesquisa
17.911328%
The paper wants to understand the assimilation pattern of foreign migrants in Italy. Three novelties characterize this study. First, the research compares the wage assimilation of international migrants with both internal migrants and local natives in Italy, a country with substantial internal and international migration. This comparison, never exploited before, provides indirect evidence for the role played by language and knowledge of social capital in the assimilation of foreign migrants relative to both natives and internal migrants. Second, we inquired into the possible causes of under-assimilation by controlling for the date of entry and migrant sector concentration. Third, we model new corrections of the selection bias due to return migration. The correction for the selection bias is introduced in the wage equation through a duration extension of the traditional Heckman correction term and alternatively through a hazard rate correction. The empirical test uses the Italian administrative dataset on dependent employment (WHIP), to estimate a fixed effect model for the weekly wages of males aged 18-45 with controls for selection in return migration and unobserved heterogeneity. The three groups of workers start their careers at the same wage level. But...

## ‣ Testing for sample selection in pseudo panels : theory and Monte Carlo

Mora, Jhon James; Muro, Juan
Tipo: ﻿info:eu-repo/semantics/workingPaper Formato: 835110 bytes; application/pdf
Português
Relevância na Pesquisa
38.361343%
Sample selection bias is commonly used in economic models based on micro data. Despite the continuous generalization of panel data surveys, most countries still collect microeconomic information on the behavior of economic agents by means of repeated independent and representative cross-sections. This paper discusses a simple testing procedure for sample selection bias in pseudo panels. In the context of conditional mean independence panel data models we describe a pseudo panel model in which under convenient expansion of the original specification with a selectivity bias correction term the method allows us to use a Wald test of H0: as a test of the null hypothesis of absence of sample selection bias. We show that the proposed selection bias correction term is proportional to Inverse Mills ratio with an argument equal to the normit of a consistent estimation of the observed proportion of individuals in each cohort. This finding can be considered a cohort counterpart of Heckmans selectivity bias correction for the individual case and generalizes to some extent previous existing results in the empirical labour literature. Monte Carlo analysis shows the test does not reject the null for fixed T at a 5% significance level in finite samples and increases its power when utilizing cohort size corrections as suggested by Deaton (1985). As a side effect...

## ‣ Building or Bypassing Recipient Country Systems : Are Donors Defying the Paris Declaration?

Knack, Stephen
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
Tipo: Publications & Research :: Policy Research Working Paper; Publications & Research
Português
Relevância na Pesquisa
27.707227%
The 2005 Paris Declaration on Aid Effectiveness sets targets for increased use by donors of recipient country systems for managing aid. It also calls for donors to be more responsive to the quality of recipient country systems: the optimal level of their use, in terms of maximizing the development effectiveness of aid, is believed to vary with their quality. This study investigates the degree to which donors' use of country systems is in fact positively related to their quality, using indicators explicitly endorsed for this purpose by the Paris Declaration and covering the 2005-2010 period. The results of these tests strongly confirm a positive and significant relationship, and show it is robust to corrections for potential sample selection, omitted variables, or endogeneity bias. The result holds even when estimates are informed only by variation over time within each donor-recipient pair in use and quality of country systems. Moreover, donor-specific tests show that use of country systems varies positively with their quality for the vast majority of donors. These findings contradict several other studies that claim there is no relation and imply that donors in this respect are failing to live up to their commitments under the Paris Declaration. The author's interpretation of the available evidence on use of country systems is more favorable: donors' behavior over the measurement period is largely consistent with their commitments in this area. In this respect...

## ‣ Are There Lasting Impacts of Aid to Poor Areas? Evidence from Rural China

Chen, Shaohua; Mu, Ren; Ravallion, Martin
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
Tipo: Publications & Research :: Policy Research Working Paper; Publications & Research
Português
Relevância na Pesquisa
27.833574%
The paper revisits the site of a large, World Bank-financed, rural development program in China 10 years after it began and four years after disbursements ended. The program emphasized community participation in multi-sectoral interventions (including farming, animal husbandry, infrastructure and social services). Data were collected on 2,000 households in project and nonproject areas, spanning 10 years. A double-difference estimator of the program's impact (on top of pre-existing governmental programs) reveals sizeable short-term income gains that were mostly saved. Only modest gains to mean consumption emerged in the longer term-in rough accord with the gain to permanent income. Certain types of households gained more than others. The educated poor were under-covered by the community-based selection process-greatly reducing overall impact. The main results are robust to corrections for various sources of selection bias, including village targeting and interference due to spillover effects generated by the response of local governments to the external aid.

## ‣ Determinants of hospital tax-exempt debt yields: corrections for selection and simultaneous equation bias.

Carpenter, C E
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.537373%
The cost of capital for hospitals is a topic of continuing interest as Medicare's new capital payment policy is implemented. This study examines the determinants of tax-exempt revenue bond yields, the primary source of long-term capital for hospitals. Two important methodological issues are addressed. A probit analysis estimates the probability that a hospital or system will be observed in the tax-exempt market. A selection-corrected two-stage least squares analysis allows for the simultaneous determination of bond yield and bond size. The study is based on a sample of hospitals that issued tax-exempt revenue bonds in 1982-1984, the years immediately surrounding implementation of Medicare's new payment system based on diagnosis-related groups, and an equal number of hospitals not in the market during the study period. Results suggest that hospital systems and hospitals with high occupancy rates are most likely to enter the tax-exempt revenue bond market. The yield equation suggests that hospital-specific variables may not be good predictors of the cost of capital once estimates are corrected for selection.

## ‣ Weak lensing power spectra for precision cosmology: Multiple-deflection, reduced shear and lensing bias corrections

Krause, Elisabeth; Hirata, Christopher M.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.84247%
It is usually assumed that the ellipticity power spectrum measured in weak lensing observations can be expressed as an integral over the underlying matter power spectrum. This is true at second order in the gravitational potential. We extend the standard calculation, constructing all corrections to fourth order in the gravitational potential. There are four types of corrections: corrections to the lensing shear due to multiple-deflections; corrections due to the fact that shape distortions probe the reduced shear $\gamma/(1-\kappa)$ rather than the shear itself; corrections associated with the non-linear conversion of reduced shear to mean ellipticity; and corrections due to the fact that observational galaxy selection and shear measurement is based on galaxy brightnesses and sizes which have been (de)magnified by lensing. We show how the previously considered corrections to the shear power spectrum correspond to terms in our analysis, and highlight new terms that were not previously identified. All correction terms are given explicitly as integrals over the matter power spectrum, bispectrum, and trispectrum, and are numerically evaluated for the case of sources at z=1. We find agreement with previous works for the ${\mathcal O}(\Phi^3)$ terms. We find that for ambitious future surveys...

## ‣ Bias in the Estimation of Global Luminosity Functions

Ilbert, O.; Tresse, L.; Arnouts, S.; Zucca, E.; Bardelli, S.; Zamorani, G.; Adami, C.; Cappi, A.; Garilli, B.; Fevre, O. Le; Maccagni, D.; Meneux, B.; Scaramella, R.; Scodeggio, M.; Vettolani, G.; Zanichelli, A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
28.189492%
We discuss a bias present in the calculation of the global luminosity function (LF) which occurs when analysing faint galaxy samples. This effect exists because of the different spectral energy distributions of galaxies, which are in turn quantified by the k-corrections. We demonstrate that this bias occurs because not all galaxy types are visible in the same absolute magnitude range at a given redshift and it mainly arises at high redshift since it is related to large k-corrections. We use realistic simulations with observed LFs to investigate the amplitude of the bias. We also compare our results to the global LFs derived from Hubble Deep Field-North and -South (HDF) surveys. We conclude that, as expected, there is no bias in the global LF measured in the absolute magnitude range where all galaxy types are observable. Beyond this range the faint-end slope of the global LF can be over/under-estimated depending on the adopted LF estimator. The effect is larger when the reference filter in which the global LF is measured, is far from the rest-frame filter in which galaxies are selected. The fact that LF estimators are differently affected by this bias implies that the bias is minimal when the different LF estimators give measurements consistent with one another at the faint-end. For instance...

## ‣ Lensing Corrections to Features in the Angular Two-Point Correlation Function and Power Spectrum

LoVerde, Marilena; Hui, Lam; Gaztanaga, Enrique
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
28.283362%
It is well known that magnification bias, the modulation of galaxy or quasar source counts by gravitational lensing, can change the observed angular correlation function. We investigate magnification-induced changes to the shape of the observed correlation function w(\theta) and the angular power spectrum C_{\ell}, paying special attention to the matter-radiation equality peak and the baryon wiggles. Lensing mixes the correlation function of the source galaxies with the matter correlation at the lower redshifts of the lenses. Since the lenses probe structure nearer to the observer, the angular scale dependence of the lensing terms is different from that of the sources, thus the observed correlation function is distorted. We quantify how the lensing corrections depend on the width of the selection function, the galaxy bias b, and the number count slope s. The correction increases with redshift and larger corrections are present for sources with steep number count slopes and/or broad redshift distributions. The most drastic changes to C_{\ell} occur for measurements at z >~1.5 and \ell <~ 100. For the source distributions we consider, magnification bias can shift the matter-radiation equality scale by 1-6% at z ~ 1.5 and by z ~ 3.5 the shift can be as large as 30%. The baryon bump in \theta^2w(\theta) is shifted by <~ 1% and the width is typically increased by ~10%. Shifts of >~ 0.5% and broadening of >~ 20% occur only for very broad selection functions and/or galaxies with (5s-2)/b>~2. However...

## ‣ Bias Properties of Extragalactic Distance Indicators.XI. Methods to Correct for Observational Selection Bias for RR Lyrae Absolute Magnitudes from Trigonometric Parallaxes Expected from the FAME Astrometric Satellite

Sandage, Allan; Saha, A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
28.172688%
Please note that this abstract has been shortened from that found in the paper. A brief history is given of the development of the correction for observation selection bias inherent in the calibration of absolute magnitudes using trigonometric parallaxes. As a tutorial to gain an intuitive understanding of several complicated trigonometric bias problems, we study a toy bias model of a parallax catalog which incorporates assumed parallax measuring errors of various severities. The two effects of bias errors on the derived absolute magnitudes are (1) the Lutz-Kelker correction itself that depends on the fractional parallax error and the spatial distribution, and (2) a Malmquist-like incompleteness' correction of opposite sign due to various apparent magnitude cut-offs as they are progressively imposed on the catalog. The simulations involve 3 million stars spread with varying density distributions in a volume bounded by a radius of 50,000 pc. A fixed absolute magnitude of M_V = +0.6 is used to imitate RR Lyrae variables in the mean. The bias is demonstrated for various assumed spatial densities and parallax error models, including one that is projected for the FAME satellite. The effects of imposing magnit ude limits and limits on the observer's' error are displayed. We contrast the method of calculating mean absolute magnitude directly from the parallaxes where bias corrections are mandatory...

## ‣ Performance analysis and optimal selection of large mean-variance portfolios under estimation risk

Rubio, Francisco; Mestre, Xavier; Palomar, Daniel P.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.169814%
We study the consistency of sample mean-variance portfolios of arbitrarily high dimension that are based on Bayesian or shrinkage estimation of the input parameters as well as weighted sampling. In an asymptotic setting where the number of assets remains comparable in magnitude to the sample size, we provide a characterization of the estimation risk by providing deterministic equivalents of the portfolio out-of-sample performance in terms of the underlying investment scenario. The previous estimates represent a means of quantifying the amount of risk underestimation and return overestimation of improved portfolio constructions beyond standard ones. Well-known for the latter, if not corrected, these deviations lead to inaccurate and overly optimistic Sharpe-based investment decisions. Our results are based on recent contributions in the field of random matrix theory. Along with the asymptotic analysis, the analytical framework allows us to find bias corrections improving on the achieved out-of-sample performance of typical portfolio constructions. Some numerical simulations validate our theoretical findings.

## ‣ The WiggleZ Dark Energy Survey: the selection function and z=0.6 galaxy power spectrum

Blake, Chris; Brough, Sarah; Colless, Matthew; Couch, Warrick; Croom, Scott; Davis, Tamara; Drinkwater, Michael J.; Forster, Karl; Glazebrook, Karl; Jelliffe, Ben; Jurek, Russell J.; Li, I-hui; Madore, Barry; Martin, Chris; Pimbblet, Kevin; Poole, Gregory
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.537373%
We report one of the most accurate measurements of the three-dimensional large-scale galaxy power spectrum achieved to date, using 56,159 redshifts of bright emission-line galaxies at effective redshift z=0.6 from the WiggleZ Dark Energy Survey at the Anglo-Australian Telescope. We describe in detail how we construct the survey selection function allowing for the varying target completeness and redshift completeness. We measure the total power with an accuracy of approximately 5% in wavenumber bands of dk=0.01 h/Mpc. A model power spectrum including non-linear corrections, combined with a linear galaxy bias factor and a simple model for redshift-space distortions, provides a good fit to our data for scales k < 0.4 h/Mpc. The large-scale shape of the power spectrum is consistent with the best-fitting matter and baryon densities determined by observations of the Cosmic Microwave Background radiation. By splitting the power spectrum measurement as a function of tangential and radial wavenumbers we delineate the characteristic imprint of peculiar velocities. We use these to determine the growth rate of structure as a function of redshift in the range 0.4 < z < 0.8, including a data point at z=0.78 with an accuracy of 20%. Our growth rate measurements are a close match to the self-consistent prediction of the LCDM model. The WiggleZ Survey data will allow a wide range of investigations into the cosmological model...

## ‣ A Bayesian Monte-Carlo Analysis of the M-sigma Relation

Morabito, Leah; Dai, Xinyu
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
18.281434%
We present an analysis of selection biases in the M-sigma relation using Monte- Carlo simulations including the sphere of influence resolution selection bias and a selection bias in the velocity dispersion distribution. We find that the sphere of influence selection bias has a significant effect on the measured slope of the M-sigma relation, modeled as \beta_intrinsic = -4.69 + 2.22\beta_measured, where the measured slope is shallower than the model slope in the parameter range of \beta > 4, with larger corrections for steeper model slopes. Therefore, when the sphere of influence is used as a criterion to exclude unreliable measurements, it also in- troduces a selection bias that needs to be modeled to restore the intrinsic slope of the relation. We find that the selection effect due to the velocity dispersion distribution of the sample, which might not follow the overall distribution of the population, is not important for slopes of \beta ~ 4-6 of a logarithmically linear M-sigma relation, which could impact some studies that measure low (e.g., \beta < 4) slopes. Combining the selection biases in velocity dispersions and the sphere of influence cut, we find the uncertainty of the slope is larger than the value without modeling these effects...

## ‣ The WiggleZ Dark Energy Survey: the selection function and z = 0.6 galaxy power spectrum

Blake, Chris; Brough, Sarah; Colless, Matthew; Couch, Warrick; Croom, Scott; Davis, Tamara; Drinkwater, Michael J.; Forster, Karl; Glazebrook, Karl; Jelliffe, Ben; Jurek, Russell J.; Li, I-hui; Madore, Barry; Martin, Chris; Pimbblet, Kevin; Poole, Gregory
Fonte: Royal Astronomical Society Publicador: Royal Astronomical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Relevância na Pesquisa
27.537373%
We report one of the most accurate measurements of the three-dimensional large-scale galaxy power spectrum achieved to date, using 56 159 redshifts of bright emission-line galaxies at effective redshift z ≈ 0.6 from the WiggleZ Dark Energy Survey at the Anglo-Australian Telescope. We describe in detail how we construct the survey selection function allowing for the varying target completeness and redshift completeness. We measure the total power with an accuracy of approximately 5 per cent in wavenumber bands of Δk= 0.01 h Mpc^(−1). A model power spectrum including non-linear corrections, combined with a linear galaxy bias factor and a simple model for redshift-space distortions, provides a good fit to our data for scales k < 0.4 h Mpc^(−1). The large-scale shape of the power spectrum is consistent with the best-fitting matter and baryon densities determined by observations of the cosmic microwave background radiation. By splitting the power spectrum measurement as a function of tangential and radial wavenumbers, we delineate the characteristic imprint of peculiar velocities. We use these to determine the growth rate of structure as a function of redshift in the range 0.4 < z < 0.8, including a data point at z= 0.78 with an accuracy of 20 per cent. Our growth rate measurements are a close match to the self-consistent prediction of the Λ cold dark matter model. The WiggleZ survey data will allow a wide range of investigations into the cosmological model...

## ‣ Weak lensing power spectra for precision cosmology : Multiple-deflection, reduced shear, and lensing bias corrections

Krause, E.; Hirata, C. M.
Fonte: EDP Sciences Publicador: EDP Sciences
Tipo: Article; PeerReviewed Formato: application/pdf
Relevância na Pesquisa
27.84247%
It is usually assumed that the ellipticity power spectrum measured in weak lensing observations can be expressed as an integral over the underlying matter power spectrum. This is true at order O(Φ^2) in the gravitational potential. We extend the standard calculation, constructing all corrections to order O(Φ^4). There are four types of corrections: corrections to the lensing shear due to multiple-deflections; corrections due to the fact that shape distortions probe the reduced shear γ/(1 − κ) rather than the shear itself; corrections associated with the non-linear conversion of reduced shear to mean ellipticity; and corrections due to the fact that observational galaxy selection and shear measurement is based on galaxy brightnesses and sizes which have been (de)magnified by lensing. We show how the previously considered corrections to the shear power spectrum correspond to terms in our analysis, and highlight new terms that were not previously identified. All correction terms are given explicitly as integrals over the matter power spectrum, bispectrum, and trispectrum, and are numerically evaluated for the case of sources at z = 1. We find agreement with previous works for the O(Φ^3) terms. We find that for ambitious future surveys...

## ‣ O atrito nas pesquisas longitudinais: o caso da pesquisa mensal de emprego (PME/IBGE)

Ribas, Rafael Perez; Soares, Sergei Suarez Dillon
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Formato: application/pdf