Is neglected heterogeneity really an issue in binary and fractional regression models? A simulation exercise for logit, probit and loglog models

In this paper we examine theoretically and by simulation whether or not unobserved heterogeneity independent of the included regressors is really an issue in logit, probit and loglog models with both binary and fractional data. We found that unobserved heterogeneity: (i) produces an attenuation bias in the estimation of regression coefficients; (ii) is innocuous for logit estimation of average sample partial effects, while in the probit and loglog cases there may be important biases in the estimation of those quantities; (iii) has much more destructive effects over the estimation of population partial effects; (iv) only for logit models does not affect substantially the prediction of outcomes; and (v) is innocuous for the size and consistency of Wald tests for the significance of observed regressors but, in small samples, reduces their power substantially.Binary models; fractional models; neglected heterogeneity; partial effects; prediction; wald tests.

Virtual bilepton effects in polarized Moller scattering

We investigate the indirect effects of heavy vector bileptons being exchanged in polarized Moller scattering, at the next generation of linear colliders. Considering both longitudinal and transverse beam polarization, and accounting for initial-state radiation, beamstrahlung and beam energy spread, we discuss how angular distributions and asymmetries can be used to detect clear signals of virtual bileptons, and the possibility of distinguishing theoretical models that incorporate these exotic particles. We then estimate 95% C.L. bounds on the mass of these vector bileptons and on their couplings to electrons.Comment: 19 pages, 10 figure

Nonparametric models of financial leverage decisions

This paper investigates the properties of nonparametric decision tree models in the analysis of financial leverage decisions. This approach presents two appealing features: the relationship between leverage ratios and the explanatory variables is not predetermined but is derived according to information provided by the data, and the models respect the bounded and fractional nature of leverage ratios. The analysis shows that tree models suggest relationships between explanatory variables and the relative amount of issued debt that parametric models fail to capture. Furthermore, the significant relationships found by tree models are in most cases in accordance with the effects predicted by the pecking-order theory. The results also show that two-part tree models can accommodate better the distinct effects of explanatory variables on the decision to issue debt and on the amount of debt issued by firms that do resort to debt.Capital structure, Fractional regression, Decision trees, Two-part models

A symptotic Bias for GMM and GEL Estimators with Estimated Nuisance Parameter

This papers studies and compares the asymptotic bias of GMM and generalized empirical likelihood (GEL) estimators in the presence of estimated nuisance parameters. We consider cases in which the nuisance parameter is estimated from independent and identical samples. A simulation experiment is conducted for covariance structure models. Empirical likelihood offers much reduced mean and median bias, root mean squared error and mean absolute error, as compared with two-step GMM and other GEL methods. Both analytical and bootstrap bias-adjusted two-step GMM estima-tors are compared. Analytical bias-adjustment appears to be a serious competitor to bootstrap methods in terms of finite sample bias, root mean squared error and mean absolute error. Finite sample variance seems to be little affected

Hope, home and insecurity: Gendered labours of resilience among the urban poor of Metro Cebu, the Philippines

This article traces the labours of hope embedded in the everyday social reproductive practices of urban poor homeowner association members in Metro Cebu, the Philippines. It explores how aspirations for housing and land tenure security and the (failed) promises of opportunity bound in the urban materialise in the narratives and activities of women and men living in informal settlements. I argue that the sociality of hope, which propels and sustains homeowner associations, produces gendered labours of resilience amidst everyday circumstances of poverty, uncertainty, risk and displacement. As I reveal, these care-based practices constitute expressions of hope that are driven by moral codes associated with the family, industriousness and service to others. These findings reinforce the utility of hope as an analytical lens in geographical studies; one which broadens conceptualisations of labour beyond economic production to include, in this case, the emotional embodiments and reproductive activities that underpin people’s everyday resilience

Moment-based estimation of nonlinear regression models with boundary outcomes and endogeneity, with applications to nonnegative and fractional responses

In this article, we suggest simple moment-based estimators to deal with unobserved heterogeneity in a special class of nonlinear regression models that includes as main particular cases exponential models for nonnegative responses and logit and complementary loglog models for fractional responses. The proposed estimators: (i) treat observed and omitted covariates in a similar manner; (ii) can deal with boundary outcomes; (iii) accommodate endogenous explanatory variables without requiring knowledge on the reduced form model, although such information may be easily incorporated in the estimation process; (iv) do not require distributional assumptions on the unobservables, a conditional mean assumption being enough forconsistentestimationofthestructuralparameters;and(v)undertheadditionalassumption that the dependence between observables and unobservables is restricted to the conditional mean, produce consistent estimators of partial effects conditional only on observables.info:eu-repo/semantics/publishedVersio

Engendering disaster risk management and resilience-building: The significance of the everyday in evaluations of the exceptional

This article argues for greater consideration of ‘the everyday’ within evaluations of ‘the exceptional’ and presents this as a practical means of engendering disaster risk reduction and management (DRRM) and resilience-building. Building on scholarship from feminist geography, gender and development and feminist political ecology, it charts a new way of theorising disaster risk and resilience from a gendered perspective through the analytic of the everyday, and substantiates this with findings from ethnographic research conducted between 2016 and 2017 in disaster-prone informal settlements in the Philippines. As this case reveals, a focus on the everyday helps to uncover the multiple subjective embodiments of risk and insecurity and the structural systems that underpin related inequalities and exclusions. Crucially, the lens of ‘the everyday’ also exposes the social reproductive labours and power hierarchies embedded in community-based DRRM and resilience-building programmes; insights which are vital to advancing more inclusive, sustainable and socially just approaches to disaster risk governance and climate change adaptation

Intensidad de la Senal ˜ en T1 en el Núcleo Dentado Tras la Administración del Agente de Contraste con Gadolinio Macrocíclico Gadoterato de Meglumina: un Estudio Observacional

Introduction and aims: Contradictory results have been reported about hyperintensity of the globus pallidus and/or dentate nucleus on unenhanced T1-weighted magnetic resonance (MR) images after exposure to various gadolinium-based contrast agents. This change in signal intensity varies with different gadolinium-based contrast agents. We aimed to determine whether signal intensity in the dentate nucleus is increased in unenhanced T1-weighted images in patients who have undergone multiple studies with the macrocyclic gadolinium-based contrast agent gadoterate meglumine. We thoroughly reviewed the literature to corroborate our results. Materials and methods: We included patients who had undergone more than 10 MR studies with gadoterate meglumine. We quantitatively analyzed the signal intensity in unenhanced T1-weighted MR images measured in regions of interest placed in the dentate nucleus and the pons, and we calculated the dentate nucleus-to-pons signal intensity ratios and the differences between the ratio in the first MR study and the last MR study. We used t-tests to evaluate whether the differences between the signal intensity ratios were different from 0. We also analyzed the subgroups of patients who had been administered <15 and ≥15 doses of gadoterate meglumine. We used Pearson correlation to determine the relationships between the differences in the signal intensity ratios and the number of doses of gadoterate meglumine administered. Results: The 54 patients (26 men) had received a mean of 13.8±3.47 doses (range, 10-23 doses). The difference in the dentate nucleus-pons signal intensity ratio between the first and last MR study was -0.0275±0.1917 (not significantly different from 0; p=0.2968) in the entire group, -0.0357±0.2204 (not significantly different from 0; p = 0.351 in the patients who had received <15 doses (n=34), and -0.0135±0.1332 (not significantly different from 0; p = 0.655) in those who had received ≥15 doses (n=20). Differences in signal intensity ratios did not correlate significantly with the accumulated dose of gadoterate meglumine (P = 0.9064; ρ = -0.0164 [95%]). Conclusions: Receiving more than 10 doses of gadoterate meglumine was not associated with increased signal intensity in the dentate nucleus.Introducción y objetivo: Se han notificado resultados contradictorios sobre un aumento en la intensidad de la se˜nal (IS) en las imágenes de resonancia magnética (RM) ponderadas en T1 no realzadas en el globo pálido y/o el núcleo dentado (ND) después de la exposición a varios agentes de contraste con gadolinio (ACG). Este cambio en la se˜nal varía en función del ACG específico. Nuestro objetivo fue investigar si existe un aumento en la IS del ND en imágenes ponderadas en T1 no realzadas en pacientes sometidos a múltiples administraciones del ACG macrocíclico gadoterato de meglumina. Se realizó una revisión exhaustiva de la bibliografía para corroborar nuestros resultados. Materiales y métodos: Se incluyeron pacientes que se habían sometido a más de 10 estudios de RM con contraste y administración exclusiva de gadoterato de meglumina. Se llevó a cabo un análisis cuantitativo mediante el uso de mediciones de regiones de interés en el ND y el puente en imágenes no realzadas ponderadas en T1. Se calcularon las proporciones ND-puente y las diferencias en las proporciones entre el inicio y la última RM realizada. Se utilizó una prueba de la t de una muestra para evaluar si las diferencias en la proporción de la IS difieren de 0. Se realizó un análisis de subgrupos de pacientes con <15 y ≥15 dosis. Se utilizó el análisis de correlación de Pearson para determinar las correlaciones entre las diferencias de las proporciones de la IS y el número de administraciones del ACG. Resultados: 54 pacientes (26 hombres) recibieron una media de 13,8 dosis ± 3,47 (desviación estándar [DE]) (rango, 10−23 dosis). La diferencia en la proporción de la IS ND-puente entre la primera y la última exploración de RM fue de -0,0275 ± 0,1917 y no difirió significativamente de 0 P = 0,2968) en el análisis general y en el análisis de subgrupos [(<15 (n = 34), -0,0357 ± 0,2204, P = 0,351 y ≥15 (n = 20), -0,0135 ± 0,1332, p = 0,655)]. Las diferencias en la proporción de la IS no se correlacionaron significativamente Pon la dosis acumulada de gadoterato de meglumina (P = 0,9064; = -0,0164 [95%]). Conclusiones: Más de 10 administraciones de gadoterato de meglumina no se asoció a un aumento de la IS en el ND.info:eu-repo/semantics/publishedVersio

Adsorption of two pesticides on a clay surface: a theoretical study

The contamination of water resources with many organic xenobiotic compounds poses a challenge to environmental sciences and technologies [1]. Although in many cases these contaminants are present only in small concentrations, the large variety of such compounds (some of which are classified as priority pollutants) is a matter of concern. Adsorption, alone or as part of a more complex water or wastewater treatment process, has been seen as playing a very important role in the removal of many of these pollutants [2]. In this regard, the choice of adsorbent materials is crucial, which requires an understanding of the details involved in the adsorption of more or less complex organic molecules by a variety of surfaces of different types. In addition to laboratory studies, computational studies may be valuable in this study [3]. MCPA (2-methyl-4-chlorophenoxyacetic acid, a herbicide) and Clofibric acid (2-(4-chlorophenoxy)-2-methylpropanoic, the metabolite of a pharmaceutical, clofibrate, and also a herbicide) are two phenoxy acids that differ only slightly in their structures. However, a quite distinct behavior in adsorption phenomena on clay materials has been observed in past studies [4]. By relating those differences with the molecules' structural features through atomistic computational studies, some insight may be gained into the respective adsorption processes of this type of compounds. In the present work quantum chemical calculations at density functional theory level have been performed to study the adsorption of MCPA and Clofibric acid by a clay surface model. Since hydration plays an important role for the adsorption process of these species, solvent effects were considered by inclusion of water molecules explicitly into the quantum chemical calculations. The deprotonated negatively charged species were found to strongly interact with the surface and the distinct behavior of both species upon adsorption was compared with experimental evidences