The complex Watson distribution and shape analysis

The complex Watson distribution is an important simple distribution on the complex sphere which is used in statistical shape analysis. We describe the density, obtain the integrating constant and provide large sample approximations. Maximum likelihood estimation and hypothesis testing procedures for one and two samples are described. The particular connection with shape analysis is discussed and we consider an application examining shape differences between normal and schizophrenic brains. We make some observations about Bayesian shape inference and finally we describe a more general rotationally symmetric family of distributions.     

Rent Control: An Economic Abomination

Rent control is a public policy which fails on both normative and positive economic grounds. In the former case, it violates all canons of equity, of both right (private property rights are sacrosanct) and left (it does not promote egalitarianism, rather, often, it enriches rich tenants and impoverishes poor landlords). In the latter, it leads to inefficiency, deterioration of rental housing, reduces incentives for upkeep and maintenance, reduces labor mobility, exacerbates landlord tenant relations, promotes housing abandonment and homelessness, and misallocates resources away from residential rental units. This sovietization of housing has effects similar to the sovietization of anything else: farming, factories, industry, forestry, whatever. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Risk Assessment for Consumers of Mourning Doves

Recreational and subsistence hunters and anglers consume a wide range of species, including birds, mammals, fish and shellfish, some of which represent significant exposure pathways for environmental toxic agents. This study focuses on the Department of Energy's (DOE'S) Savannah River Site (SRS), a former nuclear weapons production facility in South Carolina. The potential risk of contaminant intake from consuming mourning doves ( Zenaida macroura ), the most popular United States game bird, was examined under various risk scenarios. For all of these scenarios we used the mean tissue concentration of six metals (lead, mercury, cadmium, selenium, chromium, manganese) and radiocesium, in doves collected on and near SRS. We also estimated risk to a child consuming doves that had the maximum contaminant level. We used the cancer slope factor for radiocesium, the Environmental Protection Agencies UptakeBiokinetic model for lead, and published reference doses for the other metals. As a result of our risk assessments we recommend management of water levels in contaminated reservoirs so that lake bed sediments are not exposed to use by gamebirds and other terrestrial wildlife. Particularly, measures should be taken to insure that the hunting public does not have access to such a site. Our data also indicate that doves on popular hunting areas are exposed to excess lead, suggesting that banning lead shot for doves, as has been done for waterfowl, is desirable.     

Robust mixture modeling using the skew <Emphasis Type="Italic">t</Emphasis> distribution

A finite mixture model using the Student's t distribution has been recognized as a robust extension of normal mixtures. Recently, a mixture of skew normal distributions has been found to be effective in the treatment of heterogeneous data involving asymmetric behaviors across subclasses. In this article, we propose a robust mixture framework based on the skew t distribution to efficiently deal with heavy-tailedness, extra skewness and multimodality in a wide range of settings. Statistical mixture modeling based on normal, Student's t and skew normal distributions can be viewed as special cases of the skew t mixture model. We present analytically simple EM-type algorithms for iteratively computing maximum likelihood estimates. The proposed methodology is illustrated by analyzing a real data example.     

A combined estimator in the simple errors-in-variables model

A new general method of combining estimators is proposed in order to obtain an estimator with “improved” small sample properties. It is based on a specification test statistic and incorporates some well-known methods like preliminary testing. It is used to derive an alternative estimator for the slope in the simple errors-in-variables model, combining OLS and the modified instrumental variable estimator by Fuller. Small sample properties of the new estimator are investigated by means of a Monte Carlo study.     

Determinants of infant and child mortality in Kenya: an analysis controlling for frailty effects

In this paper, Weibull unobserved heterogeneity (frailty) survival models are utilized to analyze the determinants of infant and child mortality in Kenya. The results of these models are compared to those of standard Weibull survival models. The study particularly examines the extent to which child survival risks continue to vary net of observed factors and the extent to which nonfrailty models are biased due to the violation of the statistical assumption of independence. The data came from the 1998 Kenya Demographic and Health Survey. The results of the standard Weibull survival models clearly show that biodemographic factors are more important in explaining infant mortality, while socioeconomic, sociocultural and hygienic factors are more important in explaining child mortality. Frailty effects are substantial and highly significant both in infancy and in childhood, but the conclusions remain the same as in the nonfrailty models.     

Hofstede's cultural dimensions in the GCC countries: An empirical investigation

Managerial values are not the same across the world. Therefore, Multinational Corporations may be making costly decisions if they assume that corporate policies will receive the same attention, understanding or acceptance in their branches over the world. This paper applies Hofstede's four cultural dimensions to the Gulf Cooperation Council (GCC) countries. It also compares Hofstede's results with regard to these four cultural dimensions with our findings. The results of this study show that countries change. They reemphasize the concept that ethnocentric management theories have been untenable. This implies the necessity that Multinational Corporations should study the culture of the country they plan to do business with before starting the negotiations process that precedes the operations in that country and also to monitor changes in the life style of these countries over time. When Multinational Corporations become aware of the international workforce management and the differences between different cultures, they will save themselves costly troubles, loss of qualified personnel as well as loosing international customers. Therefore, it is important for Multinational Corporations to utilize management theories available to them through research and experience.The program leading to this article was supported in part by a grant from KFUPM.