Que faut‐il voir dans les écarts de rémunération entre les travailleurs immigrés des pays du Golfe: l'effet d'a priori patronaux ou la simple conséquence de coûts d'opportunité différents?

Les auteurs s'intéressent aux disparités salariales entre les différents groupes de migrants qualifiés qui travaillent en grand nombre pour le secteur privé dans les États du Conseil de coopération du Golfe. Ils se demandent notamment si la prime salariale des Occidentaux (par rapport aux travailleurs venus d'Asie ou d'autres États arabes) découle d'éventuels a priori des employeurs. L'analyse, qui repose sur des données de 2012–2014 et sur deux méthodes de décomposition classiques, infirme l'hypothèse: les caractéristiques observables relatives à la productivité expliquent entre un tiers et trois quarts des écarts; le coût d'opportunité de la migration, supérieur pour les Occidentaux, explique la portion restante.     

Bayesian palaeoclimate reconstruction

Summary.  We consider the problem of reconstructing prehistoric climates by using fossil data that have been extracted from lake sediment cores. Such reconstructions promise to provide one of the few ways to validate modern models of climate change. A hierarchical Bayesian modelling approach is presented and its use, inversely, is demonstrated in a relatively small but statistically challenging exercise: the reconstruction of prehistoric climate at Glendalough in Ireland from fossil pollen. This computationally intensive method extends current approaches by explicitly modelling uncertainty and reconstructing entire climate histories. The statistical issues that are raised relate to the use of compositional data (pollen) with covariates (climate) which are available at many modern sites but are missing for the fossil data. The compositional data arise as mixtures and the missing covariates have a temporal structure. Novel aspects of the analysis include a spatial process model for compositional data, local modelling of lattice data, the use, as a prior, of a random walk with long-tailed increments, a two-stage implementation of the Markov chain Monte Carlo approach and a fast approximate procedure for cross-validation in inverse problems. We present some details, contrasting its reconstructions with those which have been generated by a method in use in the palaeoclimatology literature. We suggest that the method provides a basis for resolving important challenging issues in palaeoclimate research. We draw attention to several challenging statistical issues that need to be overcome.     

Conservative linear programming with mixed multiple objectives

In an ordinary linear program a single objective vector is constructed and one attempts to choose a decision vector to optimize this objective. Often multiple criteria exist or exact estimates for the components of a single objective vector are not entirely clear. For these cases a conservative decision-maker may want to choose an alternative that maximizes the objective value under the worst foreseeable circumstances. Herein we develop a unified framework for applying the maximin criterion to problems with various degrees of uncertainty attached to the objective vector. Three cases are solved via linear programming: (1) Complete Information, (2) Partial Information, and (3) Total Ignorance. It is shown that the functional value of the maximin solution decreases in a convex manner with increasing uncertainty. In addition certain relationships between maximin and efficient solutions are provided. Finally, an extension to integer constrained decision variables is presented.     

Fossil fuel supplies simulation 1972–1979

Fossil fuels are an important source of energy for Ontario Hydro and purchases exceed $100 million per year. This paper describes a computer simulation of the inventory situation over an eight-year period, which is being used to assess the relationship between order flexibility and the target carry-over stocks at the beginning of each shipping season. A simple way of presenting the results for management evaluation is illustrated. Variations of the model are used to assess random influences, such as strikes, and to determine the economic balance between holding costs and stock-outs.     

Grape flavonoids and menopausal health

Grape flavonoids are members of a larger group of plant compounds called polyphenols. Epidemiological evidence relating to the traditional Mediterranean diet, which is high in polyphenols, derived from vegetables and red wine, suggests that dietary polyphenols are of benefit to health and reduce the incidence of cardiovascular disease. Overall, the evidence is promising for the benefit of grape flavonoids in the form of red wine, red grape juice and related preparations for cardiovascular risk factors. There are data to suggest a reduction in platelet activation, inflammation and low-density lipoprotein oxidation, and improvement of endothelial function with grape flavonoids. The evidence for grape flavonoids and renal function, cognition and cancer is less clear. However, it is important to note that much of this research has been carried out in animal and cell models; relatively little work has been done in humans and specifically on the health of menopausal women. There are no general safety concerns with ingestion of grape products. Obviously, consumption of red wine should be within recommended limits and it should be noted that grape juice has high sugar content. Grape flavonoids are also available as a supplement. In conclusion, it is likely that grape flavonoids do benefit the menopausal women. Further research is needed on the mode and dosage of application to maximize these benefits.     

On the influence of market structure in modelling the US copper industry

Many of the contemporary models used to describe the behavior of the mineral industries assume a competitive market i.e. one in which market price is equal to marginal production cost. One such recent model of the worldwide copper industry is the MIDAS-II model developed for the Bureau of Mines [3, 4]. This model is used to project production and prices up through the year 2000. The purpose of this paper is to demonstrate the importance of the assumed market structure in the construction of these forecasts. If the market structure of the US copper industry is assumed to be comprised of a few large firms (an oligopoly), then forecasts based upon exactly the same data base differ significantly from the competitive market assumption.     

Migrant earnings gaps in Gulf Cooperation Council countries: Employers' perceptions or opportunity costs?

This article discusses earnings differentials among skilled Western, Arab and Asian migrants, who constitute most of the private sector labour force in Gulf Cooperation Council (GCC) countries, during the period 2012–14. Using two standard decomposition methodologies, it investigates the view that Westerners are paid premium rates due to the unobserved perceptions of private employers. The results indicate that while one‐third to three‐quarters of real hourly earnings differentials are attributable to differing observed levels of productivity‐related characteristics, the remainder are due to the incorporation of higher opportunity costs for Westerners into the bargaining process. The potential effect of unobserved perceptions is found to be irrelevant to observed earnings differentials.