Bayesian analysis of screening data: Application to AIDS in blood donors

The rapid increase in the number of AIDS cases during the 1980s and the spread of the disease from the high-risk groups into the general population has created widespread concern. In particular, assessing the accuracy of the screening tests used to detect antibodies to the HIV (AIDS) virus in donated blood and determining the prevalance of the disease in the population are fundamental statistical problems. Because the prevalence of AIDS varies widely by geographic region and data on the number of infected blood donors are published regularly, Bayesian methods, which utilize prior results and update them as new data become available, are quite useful. In this paper we develop a Bayesian procedure for estimating the prevalence of a rare disease, the sensitivity and specificity of the screening tests, and the predictive value of a positive or negative screening test. We apply the procedure to data on blood donors in the United States and in Canada. Our results augment those described in Gastwirth (1987) using classical methods. Indeed, we show that the inclusion of sound prior knowledge into the statistical analysis does not yield sufficiently precise estimates of the predictive value of a positive test. Hence confirmatory testing is needed to obtain reliable estimates. The emphasis of the Bayesian predictive paradigm on prediction intervals for future data yields a valuable insight. We demonstrate that using them might have detected a decline in the specificity of the most frequently used screening test earlier than it apparently was.     

‘Are we not [Civilized] Men?’: The Formation and Devolution of Community in Northern Mexico

Abstract The paper engages several of the issues raised by Cohn and Dirks’ statement on The Nation State, Colonialism and the Technologies of Power’ (“Beyond the Fringe’1988). It presents an account of the relationship between a community of armed peasants and the state in northern Mexico. The argument is that despite cyclic periods of coincidence and antagonism between the politico-ideological projects of state and community, an historical analysis of the experience of the people and town of Namiquipa, Chihuahua, reveals certain continuities in the forging of an alternative political-cultural space, regardless of the character of the community's relationship to the state at any time. In Mexico - as everywhere - the function of the State is the maintenance of the existing order, i.e. the maintenance of social inequality. A task for the social scientist is to document and analyse the regional strategies of the State, through the study of both the federal government and the actors who receive delegated power from it…. [T]he State apparatus is also in charge of distributing differential benefits among the population. The logic of this distribution transcends rural aspects and regional boundaries and refers to the historical dynamics of the Mexican nation, which manifests itself in the configuration of the State at different periods of time and is conditioned by the existing correlation among international forces. But from such macro-political panorama one must descend to its implications for regional development (Guillermo de la Pefia 1981: 259–260). Neither the peasants nor the State is an autonomous entity. Both are associated with other complex dependencies, with other forces and pressures. Both are stratified within and divided by interests that often contradict each other. The contradiction between the peasants and the State is not the only one in the country, and thanks to a coalition of many interests, it is not even the most apparent. However, it is the essential one in the sense that the changes that would radically and basically affect the entire situation can only be generated within it (Arturo Warman 1980:7).     

ON TESTING AGAINST RESTRICTED ALTERNATIVES FOR THE VARIANCES OF GAUSSIAN MODELS

Let π₁,…,π_p be p independent normal populations with means μ₁…, μ_p and variances σ²₁,…, σ²_p respectively. Let X(n_i) be a simple random sample of size n_i from π_i, i = 1,…,p. Given the simple random samples X(n₁),…, X(n_p) from π₁,…,π_p respectively, a test has been proposed for testing the homogeneity of variances H₀: σ²₁=…σ²_p, against the restricted alternative, H₁: σ²₁≥…≥σ²_p, with at least one strict inequality. Some properties of the test are discussed and critical values are tabulated.     

Risk Assessment Criteria for Radioactive Waste Disposal

The assessment of radioactive waste disposal options in terms of the annual risk to the critical group can lead to ambiguities, which arise largely in defining what is meant by the critical group. Radically different risk estimates can be obtained, depending on whether statistical averaging is carried out before or after the critical group is located in the time dimension. The merits of two different approaches are discussed through simple thought experiments and mathematical models. A criterion based on lifetime risk to the critical group is suggested, which could be used to supplement the currently accepted annual risk Emits. The risks from both stochastic and nonstochastic radiation effects are taken into account.     

Sex education for children in a residential center.

Sex education programs for emotionally disturbed children present special problems. This article emphasizes training of child care workers and their role as teachers.     

Variation in height acceleration in the Fels growth data

The Fels growth data record at half-yearly intervals the heights of children from birth to adulthood, and are the basis for pediatricians' growth charts used throughout North America. Aspects of human growth are the subject of a large medical and statistical literature. This paper uses smoothing splines to study the variation in height acceleration. By use of a functional version of principal-components analysis, we find that variation in the acceleration curve is essentially three-dimensional in nature. Evidence for a small growth spurt between the ages of six and eight, reported for data collected in Switzerland, is examined, and little support is found for the existence of this phenomenon in the Fels data.     

Reinserting the professional into the study of globalizing professional service firms: the case of law

Abstract In discussions of the globalization of professional service firms there is an increasing recognition that understanding the ‘social construction’ of organizational architectures is essential. In this article we argue, using the management of transnational law firms as an example, that to understand effectively these social constructions we must reincorporate an understanding of the principles of professionalism into discussions. We highlight the importance of occupational autonomy to professionals and how this is likely to influence the strategies that global professional service firms use. We also point to what we term the ‘varieties of professionalism’ and the spatially variable professional projects that underlie the values and identities of lawyers. This reveals the way rational and efficient forms of organizing have to be adapted as a result of professional values and the diverse ideals and beliefs of lawyers in different international jurisdictions.     

Trajectories of functional impairment in later life.

Functional impairment trajectories in late adulthood over a decade are characterized using the Longitudinal Retirement History Study (LRHS) data set. Non-linear patterns of age-related increase in impairment are documented with longitudinal data. Subsets of panelists from the initial large, nationally representative probability sample of employed males and unmarried employed females (N = 11,000) also exhibit differential non-linear trajectories of impairment by sex, income, and educational attainment. Concurrent analysis of the relationship over a decade among sex, SES, and functional impairment suggests that in health research, both sex and SES are broad proxy variables whose usefulness for understanding health outcomes and for policy analysis would be enhanced by the specification of components.