Genotypic performance over environmental arrays: A non-linear grouping protocol

A non-linear model for examining genotypic responses across an array of environments is contrasted with the 'joint regression' formulation, and a rigorous approach to hypothesis testing using the conditional error principle is demonstrated. The model is extended to cater for situations where single straight-line response patterns fail to characterize genotypic behaviors over an environmental array: a combination of two straight lines, with slope in below-average and in above-average environments, is offered as the 1 2 simplest representation of convex and concave patterns. A protocol for classifying genotypes according to the results of hypothesis tests, i.e. H( = ) and H( = = = 1), is 1 2 1 2 presented . A doubly desirable response pattern is convex ( < 1< ), while a doubly 1 2 undesirable pattern is concave ( > 1> ). 1 2     

Spatial variation in risk of disease: a nonparametric binary regression approach

A common problem in environmental epidemiology is the estimation and mapping of spatial variation in disease risk. In this paper we analyse data from the Walsall District Health Authority, UK, concerning the spatial distributions of cancer cases compared with controls sampled from the population register. We formulate the risk estimation problem as a nonparametric binary regression problem and consider two different methods of estimation. The first uses a standard kernel method with a cross-validation criterion for choosing the associated bandwidth parameter. The second uses the framework of the generalized additive model (GAM) which has the advantage that it can allow for additional explanatory variables, but is computationally more demanding. For the Walsall data, we obtain similar results using either the kernel method with controls stratified by age and sex to match the age–sex distribution of the cases or the GAM method with random controls but incorporating age and sex as additional explanatory variables. For cancers of the lung or stomach, the analysis shows highly statistically significant spatial variation in risk. For the less common cancers of the pancreas, the spatial variation in risk is not statistically significant.     

Finite mixture models with concomitant information: assessing diagnostic criteria for diabetes

The World Health Organization (WHO) diagnostic criteria for diabetes mellitus were determined in part by evidence that in some populations the plasma glucose level 2 h after an oral glucose load is a mixture of two distinct distributions. We present a finite mixture model that allows the two component densities to be generalized linear models and the mixture probability to be a logistic regression model. The model allows us to estimate the prevalence of diabetes and sensitivity and specificity of the diagnostic criteria as a function of covariates and to estimate them in the absence of an external standard. Sensitivity is the probability that a test indicates disease conditionally on disease being present. Specificity is the probability that a test indicates no disease conditionally on no disease being present. We obtained maximum likelihood estimates via the EM algorithm and derived the standard errors from the information matrix and by the bootstrap. In the application to data from the diabetes in Egypt project a two-component mixture model fits well and the two components are interpreted as normal and diabetes. The means and variances are similar to results found in other populations. The minimum misclassification cutpoints decrease with age, are lower in urban areas and are higher in rural areas than the 200 mg dl^-1 cutpoint recommended by the WHO. These differences are modest and our results generally support the WHO criterion. Our methods allow the direct inclusion of concomitant data whereas past analyses were based on partitioning the data.     

Making the journey into the networked enterprise, Part 2

In the May issue of Physician Executive, the authors described the difficulties other industries have had with vertical integration and why so many corporations have abandoned it for other organizational structures. In this second part of the series, they explore the ways health care organizations can make the shift into integrated delivery systems, avoiding the trap of the hierarchical, vertically integrated monolithic structures that will become the dinosaurs of the future.     

Suggestions for management training of residents

In addition to having medical expertise, physicians must possess managerial skills to deal with the ever-changing business environment of the practice of medicine. This article addresses the need for management training of physicians and calls for management training during residency and medical school. It also describes one residency program's efforts to provide comprehensive management training to its residents in pathology.     

Physician career development: toward building a model

Virtually no managed care organization provides a comprehensive and integrated program for physician career development. That's the principal finding of a survey we carried out in Spring 1994 in which we interviewed several individuals who have proven instrumental in the creation of career development programs at their managed care organizations. We started our research with the hypothesis that career development programs for physicians--frequently the most highly paid category of employees and the ones often most directly involved in the delivery of health care--should parallel the mission of the organization. In many of the organizations we surveyed, the mission included clinical excellence, managerial competence, research, teaching, community service, and building shareholder equity. While each organization offered some component of career development--usually clinical improvement and management development--very few offered programs that fostered the continued professional development of physicians in other aspects of their missions. In most cases, even in organizations with stronger career development agendas, the programs were passive and were rarely linked to the overall "corporate" goal of the managed care institution. This critical disconnect makes it extremely difficult for health care organizations to develop a workable system of accountability for their career development programs.     

International labour migration statistics in Asia: an appraisal

"The present paper attempts a critical review of the data systems of seven major labour-exporting countries--Bangladesh, India, Indonesia, Pakistan, Philippines, Sri Lanka and Thailand--which account for over 90 per cent of labour outflows from Asia....Data...are discussed under separate sections focusing on limitations as well as potential for further exploitation.... For all countries reviewed here, these data significantly understate total labour outflows, and the magnitude of the error seems to vary between countries and reflect both differences relating to the coverage and efficiency of the approval and monitoring procedure. This throws serious doubts on the appropriateness of official outmigration series for cross country comparison. Frequent changes in reporting procedures also make for discrete changes and spurious shifts in data which render trend analysis quite hazardous." (SUMMARY IN FRE AND SPA)     

Bequests as a heir "disciple device."

This paper develops a model ofinter vivos gifts and bequests in a setting of moral hazard and adverse selection. Altruistic parents do not perfectly know how much effort their children make to earn their living, nor do they know their true level of ability.Inter vivos gifts take place prior to the realization of the children's earnings whereas at the moment of bequests, parents do observe them. We show that an optimal transfer policy generally uses a mix ofinter vivos gifts — deemed as more efficient — and bequests — deemed as more redistributive.We are thankful to Allessandro Cigno, Jacques Cremer, Claude d Aspremont and anonymous referees for their comments.Responsible editor: Alessandro Cigno     

Why does cancer cluster?

What do Florida sunbathers, midwestern farmers, rural black men, and Long Island women have in common? They all have higher-than-average risks for certain cancers. Researchers know that cancer clusters are usually caused by several factors. As cancer becomes America's leading cause of death, the public will be keenly interested in sorting out the causes and reducing the risks.