An economical acceptance–rejection algorithm for uniform random variate generation over constrained simplexes

This paper develops an algorithm for uniform random generation over a constrained simplex, which is the intersection of a standard simplex and a given set. Uniform sampling from constrained simplexes has numerous applications in different fields, such as portfolio optimization, stochastic multi-criteria decision analysis, experimental design with mixtures and decision problems involving discrete joint distributions with imprecise probabilities. The proposed algorithm is developed by combining the acceptance–rejection and conditional methods along with the use of optimization tools. The acceptance rate of the algorithm is analytically compared to that of a crude acceptance–rejection algorithm, which generates points over the simplex and then rejects any points falling outside the intersecting set. Finally, using convex optimization, the setup phase of the algorithm is detailed for the special cases where the intersecting set is a general convex set, a convex set defined by a finite number of convex constraints or a polyhedron.     

New tests for stochastic order with application to case control studies

It is shown that if a binary regression function is increasing then retrospective sampling induces a stochastic ordering of the covariate distributions among the responders, which we call cases, and the non-responders, which we call controls. We also show that if the covariate distributions are stochastically ordered then the regression function must be increasing. This means that testing whether the regression function is monotone is equivalent to testing whether the covariate distributions are stochastically ordered. Capitalizing on these new probabilistic observations we proceed to develop two new non-parametric tests for stochastic order. The new tests are based on either the maximally selected, or integrated, chi-bar statistic of order one. The tests are easy to compute and interpret and their large sampling distributions are easily found. Numerical comparisons show that they compare favorably with existing methods in both small and large samples. We emphasize that the new tests are applicable to any testing problem involving two stochastically ordered distributions.     

Exclusion of HIV-positive people with disabilities in the media

This current issue piece aims to address the harmful exclusion of people with disabilities in the Iranian media. In a case study, this author collected news related to statistics of HIV-positive people covered by popular news websites written in the Persian language between June 2011 and June 2012. Within the analysed electronic texts, no reference was made to the number of HIV-positive people with disabilities. Under the rubric of critical discourse analysis, one can argue that this lack of representation may also be linked to a more general level of discourse that constitutes the marginalization of people with disabilities. This damaging exclusion both legitimizes and reproduces the ideology that people with disabilities are social minorities who can be excluded to the benefit of powerful people. This current issue piece also discusses the potential negative consequences of excluding HIV-positive people with disabilities from the discourse of HIV/AIDS in the media. Ultimately, the conceivable reasons for the Iranian government failure or refusal to publish the statistics of HIV-positive people with disabilities will be provided. Studies from various countries could shed more light on the exclusion of HIV-positive people with disabilities in the media and the interplay between HIV/AIDS and disability issues.     

Evaluation of corporate governance systems by credit rating agencies

In periods of high market volatility, and in order to minimize their risks, some investors prefer to invest their funds in well-governed companies. This paper aims to describe the methodology used by rating agencies to assess corporate governance systems (CGS) and to compare agencies’ practices. More and more the shareholders and creditors incorporate mechanisms related to CGS in the assessment of risks. Using a sample of five rating agencies, we distill 51 governance criteria to two governance factors using principal components analysis. The first factor represents the “shareholders rights and board of directors”. The second one is related to “remuneration policy and convergence of interests for shareholders and managers”. We identify three different business models for the corporate governance rating process.     

Scientific Periodicals in Iran: A Systems Approach

Scientific periodicals fulfill a significant role in the communication, exchange, and sharing of scientific findings. In recent years, the Iranian Ministry of Science, Research, and Technology (MSRT) has concentrated on non-medical, scientific periodicals. The present paper offers a short history of scientific periodicals and their role in Iran. The authors further examine the current status in the Iranian Ministry of Science, Research, and Technology by using a systems approach. Scientific periodicals in Iran involve four external entities and six major subsystems, including resources, format, content, publication, refereeing, and structure. Investigation of the current failings of the periodicals in the MSRT reveals that the main orientation of the system does not facilitate scientific communication, ease of starting new periodicals, and promotion of natural development of these periodicals. The authors suggest ways to improve the status of scholarly periodicals in Iran.     

Social media and Web 2.0 for knowledge sharing in product design

Working collaboratively with internal and external partners (suppliers, customers and internal stakeholders) has been at the epicentre of product design. Knowledge sharing has been well recognised in this context. However, there is limited research that has addressed the role of social media/Web 2.0 in facilitating knowledge sharing for sense- and decision-making within product design. To address this gap, this study draws on the resource-based view (RBV) of the firm and two vignettes that relate to ‘collaborative co-design’ and ‘collaborative design-to-order’. We illustrate the role of social media/Web 2.0 in building knowledge sharing capabilities for sense- and decision-making for internal and external partners during product design. Limitations and further research into the use of social media/Web 2.0 are also discussed.     

A two-step robust estimation of the process mean using M-estimator

Parameter estimation is the first step in constructing control charts. One of these parameters is the process mean. The classical estimators of the process mean are sensitive to the presence of outlying data and subgroups which contaminate the whole data. In existing robust estimators for the process mean, the effects of the presence of the individual outliers are being considered, while, in this paper, a robust estimator is being proposed to reduce the effect of outlying subgroups as well as the individual outliers within a subgroup. The proposed estimator was compared with some classical and robust estimators of the process mean. Although, its relative efficiency is fourth among the estimators tested, its robustness and efficiency are large when the outlying subgroups are present. Evaluation of the results indicated that the proposed estimator is less sensitive to the presence of outliers and the process mean performs well when there are no individual outliers or outlying subgroups.     

What Explains the 2007–2009 Drop in Employment?

We show that deterioration in household balance sheets, or the housing net worth channel, played a significant role in the sharp decline in U.S. employment between 2007 and 2009. Counties with a larger decline in housing net worth experience a larger decline in non‐tradable employment. This result is not driven by industry‐specific supply‐side shocks, exposure to the construction sector, policy‐induced business uncertainty, or contemporaneous credit supply tightening. We find little evidence of labor market adjustment in response to the housing net worth shock. There is no significant expansion of the tradable sector in counties with the largest decline in housing net worth. Further, there is little evidence of wage adjustment within or emigration out of the hardest hit counties.     

The Siting of Radioactive Waste Faculties: What Are the Effects on Communities?1

Abstract Despite literally dozens of attempts, and the expenditure of billions of dollars, efforts to site radioactive waste disposal facilities in this country have been uniformly unsuccessful. While both researchers and policymakers continue to address reasons for these failures, little attention is being given to the consequences for the communities themselves of these intensive siting battles. Using a research framework that addresses both the sources and consequences of community conflict, we examine what is happening in four different areas currently being considered as potential hosts for either a high- or a low-level radioactive waste facility. Some degree of conflict is observed in each community, although it varies from one area to another based on such differences as potential to experience economic benefits, perceptions of class and ethnic equity, and the role of extra-local players in the controversy. We conclude that current policies lead to inequitable distributions of risk that, in turn, create “fairness” questions that are important both in explaining current patterns of conflict and in anticipating long-term consequences for the affected communities.