Application of a predictive distribution formula to Bayesian computation for incomplete data models

We consider exact and approximate Bayesian computation in the presence of latent variables or missing data. Specifically we explore the application of a posterior predictive distribution formula derived in Sweeting And Kharroubi (2003), which is a particular form of Laplace approximation, both as an importance function and a proposal distribution. We show that this formula provides a stable importance function for use within poor man’s data augmentation schemes and that it can also be used as a proposal distribution within a Metropolis-Hastings algorithm for models that are not analytically tractable. We illustrate both uses in the case of a censored regression model and a normal hierarchical model, with both normal and Student t distributed random effects. Although the predictive distribution formula is motivated by regular asymptotic theory, it is not necessary that the likelihood has a closed form or that it possesses a local maximum.     

Selecting the precision parameter prior in Dirichlet process mixture models

We consider Dirichlet process mixture models in which the observed clusters in any particular dataset are not viewed as belonging to a finite set of possible clusters but rather as representatives of a latent structure in which objects belong to one of a potentially infinite number of clusters. As more information is revealed the number of inferred clusters is allowed to grow. The precision parameter of the Dirichlet process is a crucial parameter that controls the number of clusters. We develop a framework for the specification of the hyperparameters associated with the prior for the precision parameter that can be used both in the presence or absence of subjective prior information about the level of clustering. Our approach is illustrated in an analysis of clustering brands at the magazine Which?. The results are compared with the approach of Dorazio (2009) via a simulation study.     

Optimising the queuing system for an ear, nose and throat outpatient clinic

Several authors have considered the problem of the efficient running of hospital outpatient clinics. The first solution was probably by Welch & Bailey (1952). More recent authors include Fetter & Thompson (1966), Vissers (1979), Stafford & Aggarwal (1979). The Ear, Nose and Throat outpatient clinic presents a special case due to the complex queuing structure involved, which is described in the next section. A simulation of this special clinic was undertaken, any useful theoretical results being impossible to obtain.     

Multidimensional scaling used in multivariate statistical process control

This paper considers the use of multidimensional scaling techniques in multivariate statistical process control. Principal components analysis, multiple principal components analysis, partial least squares and PARAFAC models have already been established as useful methods for such, but it should be possible to widen the portfolio of techniques to include others that come under the multidimensional scaling class. Some of these are briefly described-namely classical scaling, non-metric scaling, biplots, Procrustes analysis-and are then used on some gas transportation data provided by Transco.     

Estimating the number of clusters in a data set via the gap statistic

We propose a method (the 'gap statistic') for estimating the number of clusters (groups) in a set of data. The technique uses the output of any clustering algorithm (e.g. K -means or hierarchical), comparing the change in within-cluster dispersion with that expected under an appropriate reference null distribution. Some theory is developed for the proposal and a simulation study shows that the gap statistic usually outperforms other methods that have been proposed in the literature.     

Technology and institutions: living in a material world

This article addresses the relationship between technology and institutions and asks whether technology itself is an institution. The argument is that social theorists need to attend better to materiality: the world of things and objects of which technical things form an important class. It criticizes the new institutionalism in sociology for its failure to sufficiently open up the black box of technology. Recent work in science and technology studies (S&TS) and in particular the sociology of technology is reviewed as another route into dealing with technology and materiality. The recent ideas in sociology of technology are exemplified with the author’s study of the development of the electronic music synthesizer.

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Roads to Poverty Reduction? Exploring Rural Roads' Impact on Mobility in Africa and Asia

Within current poverty reduction programmes, focus on the social‐welfare millennium development goals is widening to embrace a concern with infrastructural investment, particularly for remote areas. The previously popular assumption that rural disadvantage can be remedied by road‐building is resurfacing. Using survey data from Ethiopia, Zambia and Vietnam, this article explores how effective such investment is in addressing mobility and social‐service accessibility in rural areas. The findings indicate that, in extremely remote areas, road improvements may catalyse the expansion of social‐service provision, as evidenced in Ethiopia. However, given the poor's relative lack of motor vehicles and ability to pay for public transport, they are, by no means, a sufficient condition for enhancing the mobility of the rural poor.     

Caribbean Exchanges: Slavery and the Transformation of English Society, 1640–1700

This article argues that the terms of identity claimed by and ascribed to Africans and their descendants in the Americas during the era of the trans-Atlantic slave trade functioned less as claims of provenance than as complicated, shifting and highly contested languages of political logic. Focusing on the ‘Kromanti’ identity associated with all major acts of resistance and maroonage in the eighteenth-century British- and Dutch-colonized Caribbean, this article connects a strategy developed by the Asante state for coping with a particular moment of beheading of the body politic in 1717 to oath-taking strategies employed by maroons of diverse origins to reconstitute viable communities. Examining the ways in which political claims were made through a language of Obeah, or social health and healing, this article argues that ritual practices comprised the discursive field of political action for eighteenth-century Africans and their descendants in Jamaica and beyond.     

The Influence of Child Protection Orientation on Child Welfare Practice

Summary This article reports the findings of the second part of a two-partresearch project examining the potential for social workersto make changes in their work with families and children. Whilstsocial workers in the United Kingdom have been encouraged toshift from a child protection to a child welfare orientationin their practice, such changes have been hampered by professionaland organizational concern to manage risk. The research exploresthe influence of a child protection orientation on practicein child welfare cases. The findings, from two file analysesand interviews with 26 social workers, indicate that such aninfluence is indeed apparent. This is evidenced in two ways;first patterns of practice in child welfare cases are similarto those in child protection cases. Secondly, while the majorityof social workers express an attitudinal desire to move towardsa child welfare orientation, they still prioritize the managementof risk in their practice. It is argued that social workersneed permission from their employing organizations to make changesin their practice. This, in turn, requires such organizationsto state clear goals in line with a child welfare orientationand develop holistic strategies to achieve these.