农业经济研究的价值

经济学家对自然科学与农业研究的价值已经进行了深入的探讨,但农业领域经济学研究的作用却鲜为人知。经济研究所提供的“产品”可分为三类:新的经济信息、促进技术进步的产品、导致政策产生的产品。每种产品的用户、影响力和效益不尽相同。我们认为,研究的作用取决于研究成果的     

Bayesian analysis of covariance under inverse Gaussian model

This paper considers the problem of analysis of covariance (ANCOVA) under the assumption of inverse Gaussian distribution for response variable from the Bayesian point of view. We develop a fully Bayesian model for ANCOVA based on the conjugate prior distributions for parameters contained in the model. The Bayes estimator of parameters, ANCOVA model and adjusted effects for both treatments and covariates along with predictive distribution of future observations are developed. We also provide the essentials for comparing adjusted treatments effects and adjusted factor effects. A simulation study and a real world application are also performed to illustrate and evaluate the proposed Bayesian model.     

Inferences on stress–strength parameter based on GLD5 distribution

Let X and Y be independent random variables distributed as generalized Lindley distribution type 5 (GLD5). This article deals with the estimation of the stress–strength parameter R = P(Y < X), which plays an important role in reliability analysis. For this purpose, the maximum likelihood and the uniformly minimum variance unbiased estimators are presented in the explicit form. Moreover, considering Arnold and Strauss’ bivariate Gamma distribution as an informative prior and Jeffreys’ as noninformative prior, the Bayes estimators are derived. Various bootstrap confidence intervals are also proposed and, finally, the presented methods are compared using a simulation study.     

Necessary and sufficient conditions for stochastic orders between (n − r + 1)-out-of-n systems in proportional hazard (reversed hazard) rates model

Consider two (n ? r + 1)-out-of-n systems, one with independent and non-identically distributed components and another with independent and identically distributed components. When the lifetimes of components follow the proportional hazard rates model, we establish a necessary and sufficient condition for the usual stochastic order to hold between the lifetimes of these two systems. For the special case of r = 2, some generalized forms of this result to the hazard rate, dispersive and likelihood ratio orders are also obtained. Moreover, for the case when the lifetimes of components follow the proportional reversed hazard rates model, we derive some similar results for comparing the lifetimes of two systems . Applications of the established results to different situations are finally illustrated.     

Some new results on aggregate claim amounts from two heterogeneous Marshall–Olkin extended exponential portfolios

In this work, we discuss some stochastic comparisons of two aggregate claim amounts. Applications of our results to the value-at-risk and tail-value-at-risk are also mentioned. It is also shown that the aggregate claim amounts of risks exhibiting a weak form of dependence known as positive cumulative dependence (negatively associated) is larger (smaller) in convex order than the corresponding aggregate claim amounts under the theoretical independence assumption. The obtained results show that the correlations between individual risks increase stop-loss premiums corresponding to aggregate claim amounts. The results established here complete and extend the results of Barmalzan, Payandeh Najafabadi, and Balakrishnan (2017 Barmalzan, G., A. T. Payandeh Najafabadi, and N. Balakrishnan. 2017. Ordering results for aggregate claim amounts from two heterogeneous Marshall–Olkin extended exponential portfolios and their applications in insurance analysis. Theory of Probability and its Applications(to appear). [Google Scholar], Theory of Probability and its Applications, to appear).     

«Il n'y a pas d’avenir dans ce métier.» Être chauffeur de VTC en Afrique par temps de pandémie

Si les plateformes ont donné du travail à beaucoup d’Africains, les emplois créés sont de mauvaise qualité, comme la pandémie l'a bien montré. Dans ce contexte, les auteurs examinent la situation particulière des chauffeurs VTC en Afrique en s'appuyant sur des entretiens approfondis, réalisés au Kenya, et sur les méthodes de l'ethnographie virtuelle. Ils montrent que ces travailleurs ont recours à un «régime de débrouille», associant résilience, réajustement et résistance. Pour améliorer les conditions de travail et lutter contre la précarité dans le secteur, il faut à la fois que les pouvoirs publics instaurent des cadres réglementaires et que les travailleurs se mobilisent collectivement.     

Correlated equilibrium in a nutshell

We analyze the concept of correlated equilibrium in the framework of two-player two-strategy games. This simple framework makes it possible to clearly demonstrate the characteristic features of this concept. We develop an intuitive and easily memorizable test for equilibrium conditions and provide a complete classification of symmetric correlated equilibria in symmetric games.     

The Challenge of Agricultural Sustainability for Asia and Europe

It is expected that climate change (CC), growing population, increasing urbanization and improving living standards are amongst the major drivers influencing future agricultural development needs. Under conventional agricultural systems, the main sources of growth in crop production are well known. Beyond suffering its consequences, agriculture has been shown to act as a driver of CC, primarily through the production and release of about 15% of the atmospheric greenhouse gases but also by altering the resilience of the agro-ecosystems. The main criterion for the production systems called conservation agriculture (CA) is the provision of an optimum environment in the root-zone to maximum possible depth. Under CA the water-holding capacity of the soil increases, and water losses are reduced. CA combined with other complementary techniques can also help reduce the emissions for methane and nitrous oxides and at the same time it can improve rural and socio-economic development.