715 research outputs found
Parametric and semiparametric estimation of ordered response models with sample selection and individual-specific thresholds
This paper provides a set of new Stata commands for parametric and semiparametric estimation of an extended version of ordered response models that accounts for both sample selection problems and heterogeneity in the thresholds for the latent variable. The standard estimator of ordered response models is therefore generalized along three directions. First, we account for the presence of endogenous selectivity effects that may lead to inconsistent estimates of the model parameters. Second, we control for both observed and unobserved heterogeneity in response scales by allowing the thresholds to depend on a set of covariates and a random individual effect. Finally, we consider two alternative specifications of the model, one parametric and one semiparametric. In the former, the error terms are assumed to follow a multivariate Gaussian distribution and the model parameters are estimated via maximum likelihood. In the latter, the distribution function of the error terms is instead approximated by following Gallant and Nychka (1997), and the model parameters are estimated via pseudo–maximum likelihood. After discussing identification and estimation issues, we present an empirical application using the second wave of the Survey on Health, Ageing and Retirement in Europe (SHARE). Specifically, we estimate an ordered response model for self-reported health on different domains by accounting for both sample selection bias due to survey nonresponse and reporting bias in the self-assessments of health.
A systematic analysis of the XMM-Newton background: III. Impact of the magnetospheric environment
A detailed characterization of the particle induced background is fundamental
for many of the scientific objectives of the Athena X-ray telescope, thus an
adequate knowledge of the background that will be encountered by Athena is
desirable. Current X-ray telescopes have shown that the intensity of the
particle induced background can be highly variable. Different regions of the
magnetosphere can have very different environmental conditions, which can, in
principle, differently affect the particle induced background detected by the
instruments. We present results concerning the influence of the magnetospheric
environment on the background detected by EPIC instrument onboard XMM-Newton
through the estimate of the variation of the in-Field-of-View background excess
along the XMM-Newton orbit. An important contribution to the XMM background,
which may affect the Athena background as well, comes from soft proton flares.
Along with the flaring component a low-intensity component is also present. We
find that both show modest variations in the different magnetozones and that
the soft proton component shows a strong trend with the distance from Earth.Comment: To appear in Experimental Astronomy. Presented at AHEAD Background
Workshop, 28-30 November 2016. Rome, Ital
A Systematic Analysis of the XMM-Newton Background: I. Dataset and Extraction Procedures
XMM-Newton is the direct precursor of the future ESA ATHENA mission. A study
of its particle-induced background provides therefore significant insight for
the ATHENA mission design. We make use of about 12 years of data, products from
the third XMM-Newton catalog as well as FP7 EXTraS project to avoid celestial
sources contamination and to disentangle the different components of the
XMM-Newton particle-induced background. Within the ESA R&D AREMBES
collaboration, we built new analysis pipelines to study the different
components of this background: this covers time behavior as well as spectral
and spatial characteristics.Comment: To appear in Experimental Astronomy, presented at AHEAD Background
Workshop, 28-30 November 2016, Rome, Italy. 12 pages, 6 figure
Changes in corneal parameters at confocal microscopy in treated glaucoma patients
The purpose of this study was to evaluate corneal parameters in treated glaucoma patients, nontreated glaucoma patients, and normal subjects using confocal microscop
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