A generalization of Jeffreys' rule for non regular models

We propose a generalization of the one-dimensional Jeffreys’ rule in order to obtain non informative prior distributions for non regular mod- els, taking into account the comments made by Jeffreys in his arti- cle of 1946. These non informatives are parameterization invariant and the Bayesian intervals have good behavior in frequentist inference. In some important cases, we can generate non informative distributions for multi-parameter models with non regular parameters. In non regular models, the Bayesian method offers a satisfactory solution to the infer- ence problem and also avoids the problem that the maximum likelihood estimator has with these models. Finally, we obtain non informative dis- tributions in job-search and deterministic frontier production homoge- nous model

La mejora de las predicciones con la inclusión de una variable agregada: aplicación a las tasas de variación del PIB de una muestra de economías europeas

El presente trabajo ilustra empíricamente cómo se pueden mejorar las predicciones de las tasas de variación, TV, del output real, PIB, de una muestra de países europeos. Esta mejora ha sido posible gracias al acceso a una base de datos de la Universidad de Groningen, que nos ha permitido calcular las tasas de variación del total de output de los países considerados. Cuando incluimos la tasa de variación total en los modelos AR(3), modelo autorregresivo con tres retardos de la tasa de variación del output de cada país, hemos observado una mejora substancial en las predicciones anuales de de las tasas de variación del output real de cada país.The present work empirically illustrates how the forecast of the annual output growth rates (GR) (where the output is the real gross domestic product (GDP)), from a sample of European countries could be improved. This improvement has been possible by means of using a database that has let us to calculate the aggregated GR of the GDP of the countries sample. When we include the common GR in the AR(3) model of each country’s data, we have observed a substantially improving of one-step-ahead forecasts of GR, due to this common variabl

Effect of shear processing on the linear viscoelastic behaviour and microstructure of bitumen/montmorillonite/MDI ternary composites

Polymer modified bitumens (PMBs) have largely been utilized as a construction material. However, lack of affinity between bitumen and polymer leads to phase separation, and eventually, performance depletion. In this paper, alternative formulations of bitumen with an organically-modified montmorillonite (OMMT) Cloisite 20A® and polymeric methylene diphenyl diisocyanate (MDI) were prepared by melt blending. Their comprehensive rheological characterization evidenced improved linear viscoelastic properties when OMMT is added, revealing a noticeable structural reinforcement and thermal stability. Rheological data also showed that MDI-involved reactions control the composite end properties, being greatly influenced by the shear conditions applied

A comparison between maximum likelihood and Bayesian estimation of stochastic frontier production models

In this paper, the finite sample properties of the maximum likelihood and Bayesian estimators of the half-normal stochastic frontier production function are analyzed and compared through a Monte Carlo study. The results show that the Bayesian estimator should be used in preference to the maximum likelihood owing to the fact that the mean square error performance is substantially better in the Bayesian framewor

Sobre la capacidad de separar los dos errores en el modelo de frontera estocástica normal/half-normal

In this paper, a simulation experiment is carried out in the framework of the normal/half -normal stochastic frontier model in order to analyse its ability to disentangle the two types of errors that form the composite error. According to the results obtained through the mean bias and the mean squared error of the parameters and efficiencies, and via Spearman rank correlation between actual and estimated efficiencies, a good performance of the model is only obtained when considering medium -sized or large samples and the variance of the inefficiencies highly contributes to that of the composite error. The problems of wrong skewness and absence of random error are also addressed. The influence on the results of selecting a wrong distribution for the inefficienc y term is also analysedEn este artículo, se lleva a cabo un experimento de simulación en el contexto del modelo con frontera estocástica normal/half -normal para analizar su capacidad de separar los dos tipos de error que forman el error compuesto. Según los resultados obtenidos a través del sesgo medio y el error cuadrático medio de los parámetros y las eficiencias, y mediante el coeficiente de correlación por rangos de Spearman entre las eficiencias reales y las estimadas, se obtiene un buen comportamiento del modelo solo cuando se consideran muestras de tamaño me diano o grande y la varianza de las ineficiencias contribuye de forma muy importante a la del error compuesto. Los problemas de la asimetría errónea y de la ausencia de errores aleatorios también son abordados. La influencia en los resultados de selecciona r una distribución errónea para el término de ineficiencia también se analiz

Algunas observaciones acerca del uso de software en la estimación del modelo Half-Normal

Using the maximum likelihood method, in order to estimate Half-Normal stochastic frontier production models, entails several practical di±culties that, perhaps, have not been su±ciently emphasised. In employing FRONTIER software, we analyse the case in which the estimation obtained suggests the absence of random factors in the composite error term. We have proved that there are reasons to doubt the validity of the parameter estimates and especially of its standard errors. On the other hand, no estimation is obtained in the previous situation, with LIMDEP software, but an error message

Bayesian estimation of the half-normal regression model with deterministic frontier

A regression model with deterministic frontier is considered. This type of model has hardly been studied, partly owing to the difficulty in the application of maximum likelihood estimation since this is a non-regular model. As an alternative, the Bayesian methodology is proposed and analysed. Through the Gibbs algorithm, the inference of the parameters of the model and of the individual efficiencies are relatively straightforward. The results of the simulations indicate that the utilized method performs reasonably wel

Phylogeny of Agavaceae Based on ndhF, rbcL, and its Sequences

Great advances have been made in our understanding of the phylogeny and classification of Agavaceae in the last 20 years. In older systems Agavaceae were paraphyletic due to overemphasis of ovary position or habit. Discovery of a unique bimodal karyotype in Agave and Yucca eventually led to a reexamination of concepts and relationships in all the lilioid monocots, which continues to the present day. Developments in cytogenetics, microscopy, phylogenetic systematics, and most recently DNA technology have led to remarkable new insights. Large-scale rbcL sequence studies placed Agavaceae with the core Asparagales and identified closely related taxa. Analysis of cpDNA restriction sites, rbcL, and ITS nrDNA sequences all supported removal of Dracaenaceae, Nolinaceae, and clarified relationships. Agavaceae s.s. presently consists of Agave, Beschorneria, Furcraea, Hesperaloe, Hesperoyucca, Manfreda, Polianthes, Prochnyanthes, and Yucca. In this paper we analyze recently obtained ndhF sequence data from Agavaceae and Asparagales and discuss the implications for classification. Parsimony analysis of ndhF data alone resolves most genera of Agavaceae and supports the inclusion of Camassia, Chlorogalum, Hesperocallis, and Hosta within Agavaceae s.l. Analysis of combined ndhF and rbcL data sets of selected Asparagales results in better resolution and stronger bootstrap support for many relationships. Combination of all available ndhF, rbcL, and ITS data in a single analysis results in the best resolution currently available for Agavaceae s.l. Implications for classification schemes past and present are discussed

Eficacia de la suplementación con β-hydroxy-β-methylbutyrate (HMB) en el deporte: actualización e implicación práctica

Introduction: although β-hydroxy-β-methylbutyrate (HMB) is generally marketed as a supplement for increasing muscle mass and strength, it is still not fully understood how and in which particular sports and conditions HMB can be more effective. Aims: the primary purpose of this review is to update and summarize the current knowledge about the usefulness of HMB and to organize this information by different sports with specific reference to sports with high wear and tear phenomena as soccer, rugby or football. Methods: a search was performed in PubMed database. This review presents the results about HMB use in sport. Results: the articles identified in this review support the notion that HMB could help to attenuate tissue catabolism and initiate muscle anabolism particularly in untrained individuals exposed to strenuous exercise or when trained individual are exposed to periods of high physical stress. HMB could therefore be applied in some specific periods of athlete’s season where there are high-intensity training periods, high density of competitions and little recovery time between them, starting recovery phases from an injury period and/or any other different situation where performance or recovery could be affected by a great catabolic environment. Conclusion: this update contributes to clarify and define possible mechanisms and/or effectiveness of HMB supplementation related to endurance sports (i.e. cycling and athletics), strength-power sports (i.e. resistance training, football, rugby, soccer, judo, waterpolo and rowing) and recreational activities.Introducción: aunque el β-hidroxi-β-metilbutirato (HMB) se ha empleado generalmente como suplemento para aumentar la masa muscular y la fuerza, es necesario un mejor entendimiento de su función y averiguar en qué deportes es más efectivo. Objetivos: el objetivo principal de esta revisión es actualizar y resumir el conocimiento existente en torno a la utilización del HMB para clasificarla en función de cada modalidad deportiva, con especial mención a aquellas actividades con un alto grado de destrucción muscular, como pueden ser el fútbol, el rugby o el fútbol americano. Métodos: se utilizó la base de datos PubMed para la búsqueda de artículos. Esta revisión presenta los resultados sobre la utilización de HMB clasificados por deportes. Resultados: la mayoría de los artículos seleccionados sugieren que cuando una persona entrenada o no entrenada se somete a un ejercicio intenso o diferente al habitual, el HMB puede atenuar el catabolismo muscular producido e iniciar los procesos anabólicos necesarios para recuperar lo antes posible. De esta forma, el HMB podría aplicarse en algunos momentos concretos de la temporada deportiva en los que hubiera períodos con entrenamientos de alta intensidad, o durante un periodo con alta densidad competitiva y con poca recuperación entre competiciones, o bien durante las primeras fases de la readaptación física después de una lesión y/o durante cualquier otra situación en la que el rendimiento o la recuperación se pueden ver afectados por un entorno altamente catabólico. Conclusión: esta revisión pretende aclarar y definir los posibles mecanismos por los que la suplementación con HMB puede ser efectiva en deportes de resistencia (ciclismo y carreras de fondo), en deportes de fuerza-potencia (fútbol, yudo, waterpolo, remo, fútbol americano y musculación) y en actividades deportivas recreacionales.This work was supported by the Andalusian Sports Medicine Centre (C.A.M.D.) through project no. EX-2005/07. FBO is granted by the Ministry of Economy and Competitiveness (RYC-2011-09011)