Alternative versions of the RESET test for binary response index models: a comparative study

Binary response index models may be affected by several forms of misspecification, which range from pure functional form problems (e.g. incorrect specification of the link function, neglected heterogeneity, heteroskedasticity) to various types of sampling issues (e.g. covariate measurement error, response misclassification, endogenous stratification, missing data). In this paper we examine the ability of several versions of the RESET test to detect such misspecifications in an extensive Monte Carlo simulation study. We find that: (i) the best variants of the RESET test are clearly those based on one or two fitted powers of the response index; and (ii) the loss of power resulting from using the RESET instead of a test directed against a specific type of misspecification is very small in many cases.Binary models; RESET; Misspecification.

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.

Alternative estimating and testing empirical strategies for fractional regression models

In many economic settings, the variable of interest is often a fraction or a proportion, being defined only on the unit interval. The bounded nature of such variables and, in some cases, the possibility of nontrivial probability mass accumulating at one or both boundaries raise some interesting estimation and inference issues. In this paper we: (i) provide a comprehensive survey of the main alternative models and estimation methods suitable to deal with fractional response variables; (ii) propose a full testing methodology to assess the validity of the assumptions required by each alternative estimator; and (iii) examine the finite sample properties of most of the estimators and tests discussed through an extensive Monte Carlo study. An application concerning corporate capital structure choices is also provided.Fractional regression models; Conditional mean tests; Non-nested hypotheses; Zero outcomes; Two-part models.

Fractional regression models for second stage DEA efficiency analyses

Data envelopment analysis (DEA) is commonly used to measure the relative efficiency of decision-making units. Often, in a second stage, a regression model is estimated to relate DEA efficiency scores to exogenous factors. In this paper, we argue that the traditional linear or tobit approaches to second-stage DEA analysis do not constitute a reasonable data-generating process for DEA scores. Under the assumption that DEA scores can be treated as descriptive measures of the relative performance of units in the sample, we show that using fractional regression models are the most natural way of modeling bounded, proportional response variables such as DEA scores. We also propose generalizations of these models and, given that DEA scores take frequently the value of unity, examine the use of two-part models in this framework. Several tests suitable for assessing the specification of each alternative model are also discussed.Second-stage DEA; Fractional data; Specification tests; One outcomes; Two-part models.

The shape of the Δ\Delta baryon in a covariant spectator quark model

Using a covariant spectator quark model that describes the recent lattice QCD data for the $\Delta$ electromagnetic form factors and all available experimental data on $\gamma N \to \Delta$ transitions, we analyze the charge and magnetic dipole distributions of the $\Delta$ baryon and discuss its shape. We conclude that the quadrupole moment of the $\Delta$ is a good indicator of the deformation and that the $\Delta^+$ charge distribution has an oblate shape. We also calculate transverse moments and find that they do not lead to unambiguous conclusions about the underlying shape.Comment: Extended introduction, references added, other small modifications. To appear in Phys. Rev. D. 14 pages, 8 figure

Discrete choice non-response

Missing values are endemic in the data sets available to econometricians. This paper suggests a unified likelihood-based approach to deal with several nonignorable missing data problems for discrete choice models. Our concern is when either the dependent variable is unobserved or situations when both dependent variable and covariates are missing for some sampling units. These cases are also considered when a supplementary random sample of observations on all covariates is available. A unified treatment of these various sampling structures is presented using a formulation of the nonresponse problems as a modification of choice-based sampling. Extensions appropriate for nonresponse are detailed of Imbens' (1992) effcient generalized method of moments (GMM) estimator for choice-based samples. Simulation evidence reveals very promising results for the various GMM estimators proposed in this paper.

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

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