Bayesian estimation of the efficient frontier

In this paper, we consider the estimation of the three determining parameters of the efficient frontier, the expected return, and the variance of the global minimum variance portfolio and the slope parameter, from a Bayesian perspective. Their posterior distribution is derived by assigning the diffuse and the conjugate priors to the mean vector and the covariance matrix of the asset returns and is presented in terms of a stochastic representation. Furthermore, Bayesian estimates together with the standard uncertainties for all three parameters are provided, and their asymptotic distributions are established. All obtained findings are applied to real data, consisting of the returns on assets included into the S&P 500. The empirical properties of the efficient frontier are then examined in detail.     

Tempered Mittag-Leffler Lévy processes

In this article, we introduce tempered Mittag-Leffler Lévy processes (TMLLP). TMLLP is represented as tempered stable subordinator delayed by a gamma process. Its probability density function and Lévy density are obtained in terms of infinite series and Mittag-Leffler function, respectively. Asymptotic forms of the tails and moments are given. A step-by-step procedure of the parameters estimation and simulation of sample paths is given. We also provide main results available for Mittag-Leffler Lévy processes (MLLP) and some extensions which are not available in a collective way in a single article. Our results generalize and complement the results available on Mittag-Leffler distribution and MLLP in several directions. Further, the asymptotic forms of the moments of the first-exit times of the TMLLP are also discussed.     

Progressive censoring with fixed censoring times

In this paper, we revisit the progressive Type-I censoring scheme as it has originally been introduced by Cohen [Progressively censored samples in life testing. Technometrics. 1963;5(3):327–339]. In fact, original progressive Type-I censoring proceeds as progressive Type-II censoring but with fixed censoring times instead of failure time based censoring times. Apparently, a time truncation has been added to this censoring scheme by interpreting the final censoring time as a termination time. Therefore, not much work has been done on Cohens's original progressive censoring scheme with fixed censoring times. Thus, we discuss distributional results for this scheme and establish exact distributional results in likelihood inference for exponentially distributed lifetimes. In particular, we obtain the exact distribution of the maximum likelihood estimator (MLE). Further, the stochastic monotonicity of the MLE is verified in order to construct exact confidence intervals for both the scale parameter and the reliability.     

Education and wage inequality in the informal sector: The case of Cameroon

This article analyses the effects of education on wage inequality in the informal sector in Cameroon. The author uses quantile regression on data from the Second survey on employment and the informal sector in Cameroon (EESI 2) of 2010. The results indicate that both wages and wage inequality increase with education in the informal sector, with tertiary education creating greatest inequality. These findings point to a number of policy recommendations for a transition to formality, such as the creation of more jobs for a skilled workforce, the development of sites adapted to informal sector activities and the creation of more vocational schools.     

信息不对称下价格随机的应急数量折扣契约研究

以市场需求和市场价格随机波动的二级供应链为研究对象,寻找其在信息不对称条件下绩效优化的路径。通过显示原理分别构建生产成本和销售成本信息不对称时应急供应链的数量折扣契约模型,得到最优订货量与最佳批发价策略。通过具体的算例加以验证,分析了信息不对称程度对供应链上成员及整个供应链绩效的影响。研究结果表明：当突发事件造成市场价格随机波动和市场需求变化时,供应链上的跟随者能从隐瞒私人信息中获利。但当市场需求增大时,整个供应链绩效受损,反之则反是。这与以往研究在市场需求随机、市场价格固定和信息不对称条件下的结论迥异。     

三级装备制造业供应链质量管理行为研究

作为我国工业化建设和国民经济发展的根本保证,供应链环境下装备制造企业的产品质量问题受到了广泛关注。本文重点考虑产品质量对供应链收益的影响,运用微分对策理论研究由单一制造商、单一部件供应商和单一零件供应商构成的三级装备制造业供应链质量管理行为的协调问题。通过对比Nash非合作博弈和Stackelberg主从博弈两种分散式决策模式及集中式决策模式下协同合作博弈的均衡结果,得到相关结论,并利用算例进行验证。研究表明,①分散式决策下,制造商的质量管理行为相同,但相比于Nash非合作博弈,Stackelberg主从博弈能够改善部件供应商和零件供应商的质量管理行为,提升供应链成员的收益水平;②集中式决策下,供应链成员的质量管理行为达到最优,系统整体收益实现最大。研究结论为装备制造业供应链成员间质量管理战略联盟的构建提供了理论依据。     

多边贸易体制下中国发展中国家地位问题研究——基于历史、现实与规范的多维考察

当前,发展中国家地位问题受到国际社会的高度关注,已成为世界贸易组织改革中的主要讨论议题。然而,现行世界贸易组织多边规则体系中并没有关于“发展中国家地位”的清晰界定,“自我认定”的方式正遭受一些国家的挑战。发展中国家地位和特殊与差别待遇条款密切相关,世界贸易组织规则体系中涵盖的155项特殊与差别待遇条款为发展中国家的国内政策提供了一定的灵活性,尽管多数为“最佳努力条款”。中国的发展中国家地位兼具身份和契约的双重属性,部分发达国家迫使中国放弃发展中国家地位,本质上旨在继续维持其在国际经济秩序中的主导地位。虽然中国的发展正处于“强起来”的第三阶段,但仍须坚持发展中国家地位不动摇。放弃发展中国家地位并不等于将获得发达国家的自动接纳,相反,还会影响到在其他国际组织和国际事务中的角色扮演,中国的发展离不开广大发展中国家的支持。当然,坚持发展中国家地位并不等于需要和其他发展中成员享受完全一致的差别待遇,在后续谈判中,中国可以保持一定的灵活性。在国际治理中,中国也将继续为国际社会的发展提供解决方案,树立负责任大国形象。     

A comparison study on modeling of clustered and overdispersed count data for multiple comparisons

Data collected in various scientific fields are count data. One way to analyze such data is to compare the individual levels of the factor treatment using multiple comparisons. However, the measured individuals are often clustered – e.g. according to litter or rearing. This must be considered when estimating the parameters by a repeated measurement model. In addition, ignoring the overdispersion to which count data is prone leads to an increase of the type one error rate. We carry out simulation studies using several different data settings and compare different multiple contrast tests with parameter estimates from generalized estimation equations and generalized linear mixed models in order to observe coverage and rejection probabilities. We generate overdispersed, clustered count data in small samples as can be observed in many biological settings. We have found that the generalized estimation equations outperform generalized linear mixed models if the variance-sandwich estimator is correctly specified. Furthermore, generalized linear mixed models show problems with the convergence rate under certain data settings, but there are model implementations with lower implications exists. Finally, we use an example of genetic data to demonstrate the application of the multiple contrast test and the problems of ignoring strong overdispersion.     

Linearity,symmetry, and equidistance in semantic differential scales for measuring images of self and images of others

ABSTRACT

Violations of linearity, symmetry, and equidistance of scale points in semantic differential scales may be due to respondents failing to figure out antonyms, to a positivity bias, or to respondents curtailing their reading the options. Multiple correspondence analysis on data provided by a randomized between-subjects experiment (split-ballot), using a web survey of 537 German residents, shows that bipolar semantic differential scales allow for linear measurement and conceal no positivity bias, and that using not suitable adjective pairs in semantic differential scales destroys symmetry.     

Inter‐country wage differences in the European Union

This article investigates the determinants of wage gaps between European Union countries along the wage distribution, applying the methodology proposed by Firpo, Fortin and Lemieux (2009) and Fortin, Lemieux and Firpo (2011). The authors conclude that both wage structure and composition effects contribute to explaining wage differentials, but that the wage structure effect is more important. This latter effect would appear to derive from differences between unknown factors, while the composition effect can largely be explained by differences in the following areas: education, proportion of workers with supervisory responsibilities, occupational structure, and, to a lesser extent, industrial structure.