Modelling data from single-photon emission computerized tomography

The completely random character of radioactive disintegration provides the basis of a strong justification for a Poisson linear model for single-photon emission computed tomography data, which can be used to produce reconstructions of isotope densities, whether by maximum likelihood or Bayesian methods. However, such a model requires the construction of a matrix of weights, which represent the mean rates of arrival at each detector of photons originating from each point within the body space. Two methods of constructing these weights are discussed, and reconstructions resulting from phantom and real data are presented.     

Physiologically Based Liver Modeling and Risk Assessment

Because of the inherent complexity of biological systems, there is often a choice between a number of apparently equally applicable physiologically based models to describe uptake and metabolism processes in toxicology or risk assessment. These models may fit the particular data sets of interest equally well, but may give quite different parameter estimates or predictions under different (extrapolated) conditions. Such competing models can be discriminated by a number of methods, including potential refutation by means of strategic experiments, and their ability to suitably incorporate all relevant physiological processes. For illustration, three currently used models for steady-state hepatic elimination--the venous equilibration model, the parallel tube model, and the distributed sinusoidal perfusion model--are reviewed and compared with particular reference to their application in the area of risk assessment. The ability of each of the models to describe and incorporate such physiological processes as protein binding, precursor-metabolite relations and hepatic zones of elimination, capillary recruitment, capillary heterogeneity, and intrahepatic shunting is discussed. Differences between the models in hepatic parameter estimation, extrapolation to different conditions, and interspecies scaling are discussed, and criteria for choosing one model over the others are presented. In this case, the distributed model provides the most general framework for describing physiological processes taking place in the liver, and has so far not been experimentally refuted, as have the other two models. These simpler models may, however, provide useful bounds on parameter estimates and on extrapolations and risk assessments.     

'Making Culture Matter': Symbolic,Spatial and Social Boundaries between Uyghurs and Han Chinese

This article illustrates how Uyghurs in the 1990s defined and reinforced contemporary Uyghur national identity in relation to Xinjiang's growing Han Chinese population. Adopting Barth's theory of fluid and negotiable ethnic boundaries, it focuses on the notion of change. While Uyghurs are currently activating and exaggerating certain religio-cultural differences--in particular the avoidance of pork--as a means of ensuring symbolic, spatial and social segregation from the Han, those criteria did not prevent interaction to the same extent in the past; nor do they prevent Uyghurs from making concessions when it benefits them to do so. It is argued that it is not religio-cultural differences per se that lie at the root of increased tensions between Uyghurs and Han Chinese, but changing social, political and economic contexts: on the one hand, growing Uyghur perceptions of socio-economic inequalities between themselves and the Han (the 'internal factor') and, on the other, the vast changes within the international political arena since the late 1980s (the 'external factor').     

Surname analysis for estimating local concentration of Hispanics and Asians

Surname analysis is a potentially useful technique for identifying members of particular racial, ethnic, or language communities within a population. We review the existing state of the art for identifying persons of Hispanic or Asian origin, based on surnames distinctive of each group. We describe the logic of surname analysis, profile several available surname dictionaries, and illustrate their applications in local redistricting. Results of our ongoing validation studies suggest promising future directions for improving accuracy and broadening applications.This article is based on a paper presented at the annual Population Association of America meetings at Cincinnati, 1 April 1993.     

Race and prevailing wage laws in the construction industry: Comment on Thieblot

Using the 1990 Census of Population, Thieblot (1999) argued that black employment and the strength of the prevailing wage laws are correlated and that repeal of these laws would lead to higher black employment in construction. Analysis of the 1970 Census of Population reveals that the relative abundance of black construction workers in the group of states that eventually would repeal their laws preceded those repeals and that this is mainly due to the characteristics of Southern labor markets. This and other research cast doubt on both the strength and the existence of such a correlation.     

Optimal sampling for repeated binary measurements

The authors consider the optimal design of sampling schedules for binary sequence data. They propose an approach which allows a variety of goals to be reflected in the utility function by including deterministic sampling cost, a term related to prediction, and if relevant, a term related to learning about a treatment effect To this end, they use a nonparametric probability model relying on a minimal number of assumptions. They show how their assumption of partial exchangeability for the binary sequence of data allows the sampling distribution to be written as a mixture of homogeneous Markov chains of order k. The implementation follows the approach of Quintana & Müller (2004), which uses a Dirichlet process prior for the mixture.