Search results for "selection"
showing 10 items of 1940 documents
Estimation de la relation de salaires de Mincer : choix de specification et enjeux économétriques
2012
In the present doctoral thesis, we estimated Mincer’s (1974) semi logarithmic wage function for the French and Pakistani labour force data. This model is considered as a standard tool in order to estimate the relationship between earnings/wages and different contributory factors. Despite of its vide and extensive use, simple estimation of the Mincerian model is biased because of different econometric problems. The main sources of bias noted in the literature are endogeneity of schooling, measurement error, and sample selectivity. We have tackled the endogeneity and measurement error biases via instrumental variables two stage least squares approach for which we have proposed two new instrum…
Selection correction in panel data models: An application to the estimation of females' wage equations
2007
In recent years a number of panel estimators have been suggested for sample selection models, where both the selection equation and the equation of interest contain individual effects which are correlated with the explanatory variables. Not many studies exist that use these methods in practise. We present and compare alternative estimators, and apply them to a typical problem in applied econometrics: the estimation of the wage returns to experience for females. We discuss the assumptions each estimator imposes on the data, and the problems that occur in our applications. This should be particularly useful to practitioners who consider using such estimators in their own application. All esti…
Scad-elastic net and the estimation of individual tourism expenditure determinants
2014
This paper introduces the use of scad-elastic net in the assessment of the determinants of individual tourist spending. This technique approaches two main estimation-related issues of primary importance. So far studies of tourism literature have made a wide use of classic regressions, whose results might be affected by multicollinearity. In addition, because of the absence of robust economic theory on tourism behavior, regressor selection is often left to researcher's choice when not driven by non-optimal automatic criteria. Scad-elastic net is an OLS model that accounts for both these problems by including two types of parameters constraints, namely the smoothly clipped absolute deviation …
Foreign capital, credit constraints and continuity of firms’ R&D
2015
ABSTRACTIn this article, we investigate the role of foreign capital participation as a means for firms to overcome the obstacle posed by credit constraints to sustain R&D investments. Using data for Spanish manufacturing firms in the period 1990–2006, we show that firms with foreign capital are significantly less likely to stop already initiated R&D projects and also more likely to sustain R&D investment when facing credit constraints. Our results are robust to positive selection into foreign capital participation, which we control through a set of variables chosen from a propensity score estimation, and to firms’ fixed-effects.
Estimation of ordered response models with sample selection
2011
We introduce two new Stata commands for the estimation of an ordered response model with sample selection. The opsel command uses a standard maximum-likelihood approach to fit a parametric specification of the model where errors are assumed to follow a bivariate Gaussian distribution. The snpopsel command uses the semi-nonparametric approach of Gallant and Nychka (1987, Econometrica 55: 363–390) to fit a semiparametric specification of the model where the bivariate density function of the errors is approximated by a Hermite polynomial expansion. The snpopsel command extends the set of Stata routines for semi-nonparametric estimation of discrete response models. Compared to the other semi-n…
Robust Estimation of Infection Fatality Rates during the Early Phase of a Pandemic
2020
AbstractDuring a pandemic, robust estimation of case fatality rates (CFRs) is essential to plan and control suppression and mitigation strategies. At present, estimates for the CFR of COVID-19 caused by SARS-CoV-2 infection vary considerably. Expert consensus of 0.1–1% covers in practical terms a range from normal seasonable Influenza to Spanish Influenza. In the following, I deduce a formula for an adjusted Infection Fatality Rate (IFR) to assess mortality in a period following a positive test adjusted for selection bias.Official datasets on cases and deaths were combined with data sets on number of tests. After data curation and quality control, a total of IFR (n=819) was calculated for 2…
Estrategias para la elaboración de modelos estadísticos de regresión
2011
Multivariable regression models are widely used in health science research, mainly for two purposes: prediction and effect estimation. Various strategies have been recommended when building a regression model: a) use the right statistical method that matches the structure of the data; b) ensure an appropriate sample size by limiting the number of variables according to the number of events; c) prevent or correct for model overfitting; d) be aware of the problems associated with automatic variable selection procedures (such as stepwise), and e) always assess the performance of the final model in regard to calibration and discrimination measures. If resources allow, validate the prediction mo…
Temporal relationship between genetic and warning signal variation in the aposematic wood tiger moth (Parasemia plantaginis).
2013
Many plants and animals advertise unpalatability through warning signals in the form of colour and shape. Variation in warning signals within local populations is not expected because they are subject to directional selection. However, mounting evidence of warning signal variation within local populations suggests that other selective forces may be acting. Moreover, different selective pressures may act on the individual components of a warning signal. At present, we have a limited understanding about how multiple selection processes operate simultaneously on warning signal components, and even less about their temporal and spatial dynamics. Here, we examined temporal variation of several w…
Changes in predator community structure shifts the efficacy of two warning signals in Arctiid moths
2013
Summary 1. Polymorphism in warning coloration is puzzling because positive frequency-dependent selection by predators is expected to promote monomorphic warning signals in defended prey. 2. We studied predation on the warning-coloured wood tiger moth (Parasemia plantaginis )b y using artificial prey resembling white and yellow male colour morphs in five separate populations with different naturally occurring morph frequencies. 3. We tested whether predation favours one of the colour morphs over the other and whether that is influenced either by local, natural colour morph frequencies or predator community composition. 4. We found that yellow specimens were attacked less than white ones rega…
Variable mode of estrus affects female decision for multiple mating
2011
Investigating patterns of variation in mating strategies may shed light on their evolutionary importance as well as their impact on the strength and shape of sexual selection. Multimale mating (polyandry) and mate choice are intensely studied subjects in the area of sexual selection, but little is known about intraspecific patterns of variation that may respond to dynamic cost-benefit balances. In a laboratory study, we investigated the mating behavior of female bank voles (Myodes glareolus) with distinctly different time and energy budgets: They were either in cycling estrus (CE) or postpartum estrus (PPE) shortly after delivery. Postpartum mating is highly constrained by time and energy d…