Eliciting expert judgements about a set of proportions

Eliciting expert knowledge about several uncertain quantities is a complex task when those quantities exhibit associations. A well-known example of such a problem is eliciting knowledge about a set of uncertain proportions which must sum to 1. The usual approach is to assume that the expert's knowledge can be adequately represented by a Dirichlet distribution, since this is by far the simplest multivariate distribution that is appropriate for such a set of proportions. It is also the most convenient, particularly when the expert's prior knowledge is to be combined with a multinomial sample since then the Dirichlet is the conjugate prior family. Several methods have been described in the literature for eliciting beliefs in the form of a Dirichlet distribution, which typically involve eliciting from the expert enough judgements to identify uniquely the Dirichlet hyperparameters. We describe here a new method which employs the device of over-fitting, i.e. eliciting more than the minimal number of judgements, in order to (a) produce a more carefully considered Dirichlet distribution and (b) ensure that the Dirichlet distribution is indeed a reasonable fit to the expert's knowledge. The method has been implemented in a software extension of the Sheffield elicitation framework (SHELF) to facilitate the multivariate elicitation process.     

Subjective Welfare, Well-Being, and Self-Reported Food Hypersensitivity in Four European Countries: Implications for European Policy

This study estimates the effects of food hypersensitivity on individuals?? perceived welfare and well-being compared to non-food hypersensitive individuals. Study respondents were recruited in the Netherlands, Poland, Spain and UK. The difference in welfare between food hypersensitive respondents and those asymptomatic to foods was estimated using a subjective welfare approach, including income evaluation. Well-being was measured using the Cantril Ladder-of-Life Scale, and health status using the Self-Perceived Health Scale. The difference in well-being, welfare and health status between participant groups was explained further using a number of background variables. No significant within-country differences in welfare between food hypersensitive respondents and respondents asymptomatic to foods were found. In terms of well-being, adult food hypersensitive respondents and their spouses reported significantly less happiness than respondents and their spouses asymptomatic to foods in the Netherlands and Poland. In Spain, the spouses of the food hypersensitive respondents were significantly less happy than respondents aymptomatic to foods. The well-being of children did not significantly differ between groups. The degree of severity of food hypersensitivity was negatively related to overall health status. In Poland, food hypersensitive respondents reported worse health status compared to asymptomatic respondents. In Spain, the converse was true. Food hypersensitive respondents were generally less happy with their life as a whole than respondents asymptomatic to foods, presumably because they experienced more negative effects, which were not related to perceived health status.     

Elicitation of multivariate prior distributions: A nonparametric Bayesian approach

In the context of Bayesian statistical analysis, elicitation is the process of formulating a prior density f(·)$f(·)$ about one or more uncertain quantities to represent a person's knowledge and beliefs. Several different methods of eliciting prior distributions for one unknown parameter have been proposed. However, there are relatively few methods for specifying a multivariate prior distribution and most are just applicable to specific classes of problems and/or based on restrictive conditions, such as independence of variables. Besides, many of these procedures require the elicitation of variances and correlations, and sometimes elicitation of hyperparameters which are difficult for experts to specify in practice. Garthwaite et al. (2005) discuss the different methods proposed in the literature and the difficulties of eliciting multivariate prior distributions. We describe a flexible method of eliciting multivariate prior distributions applicable to a wide class of practical problems. Our approach does not assume a parametric form for the unknown prior density f(·)$f(·)$, instead we use nonparametric Bayesian inference, modelling f(·)$f(·)$ by a Gaussian process prior distribution. The expert is then asked to specify certain summaries of his/her distribution, such as the mean, mode, marginal quantiles and a small number of joint probabilities. The analyst receives that information, treating it as a data set D   with which to update his/her prior beliefs to obtain the posterior distribution for f(·)$f(·)$. Theoretical properties of joint and marginal priors are derived and numerical illustrations to demonstrate our approach are given.     

Hypothesis group testing for disjoint pairs

Classical group testing (CGT) is a widely applicable biotechnical technique used to identify a small number of distinguished objects from a population when the presence of any one of these distinguished objects among a group of others produces an observable result. This paper discusses a variant of CGT called group testing for disjoint pairs (GTAP). The difference between the two is that in GTDP, the distinguished items are pairs from, not individual objects in, the population. There are several biological examples of when this abstract model applies. One biological example is DNA hybridization. The presence of pairs of hybridized DNA strands can be detected in a pool of DNA strands. Another situation is the detection of binding interactions between prey and bait proteins. This paper gives a random pooling method, similar in spirit to hypothesis testing, which identifies pairs of objects from a population that collectively have an observable function. This method is simply to apply, achieves good results, is amenable to automation and can be easily modified to compensate for testing errors. M.A. Bishop is supported by AFOSR FA8750-06-C-0007. A.J. Macula is supported by NSF-0436298, AFOSR FA8750-06-C-0007.     

A two-stage procedure to pool information across quantile levels in linear quantile regression

In linear quantile regression, the regression coefficients for different quantiles are typically estimated separately. Efforts to improve the efficiency of estimators are often based on assumptions of commonality among the slope coefficients. We propose instead a two-stage procedure whereby the regression coefficients are first estimated separately and then smoothed over quantile level. Due to the strong correlation between coefficient estimates at nearby quantile levels, existing bandwidth selectors will pick bandwidths that are too small. To remedy this, we use 10-fold cross-validation to determine a common bandwidth inflation factor for smoothing the intercept as well as slope estimates. Simulation results suggest that the proposed method is effective in pooling information across quantile levels, resulting in estimates that are typically more efficient than the separately obtained estimates and the interquantile shrinkage estimates derived using a fused penalty function. The usefulness of the proposed method is demonstrated in a real data example.     

Investigating the implementation of SME-friendly policy in public procurement

Public sector employees with responsibility for purchasing are under increasing pressure to implement small and medium enterprise (SME)-friendly policies. Such policies are intended to make it easier for SMEs to compete for and win public sector contracts. In spite of the socio-economic importance of this issue, there remains a dearth of evidence on what is happening in practice. Using primary survey data from 271 public buyers in Ireland, this paper examines the extent to which SME-friendly procurement policy is being implemented and the individual and organization factors that affect implementation. The findings reveal a gap between what government policy recommends public buyers and their organizations should do to facilitate SMEs versus what they are actually doing. Policy familiarity, procurement involvement, organization size and the maturity of the procurement function are shown to be positively associated with the implementation of SME-friendly policy. For managers and legislators, the findings underline the need to invest in the human capital dimension of public procurement if policy implementation rates are to improve.     

An Empirical Analysis of Strike Durations in Ghana from 1980 to 2004

Abstract. This paper provides a seminal analysis of strike activity for an African country in investigating the determinants of strike durations in Ghana over the period 1980–2004. The empirical approach uses a set of well‐known parametric accelerated failure time strike duration models. There is a broad consensus among the different empirical models about the role exerted on average strike duration by strike size, the rate of inflation, enterprise ownership, and political governance. However, evidence on the relationship between strike durations and business cycle activity in Ghana is less clear‐cut.     

Health Services Utilization Among Graduate Students: Patterns of Use,Access, and Satisfaction

Abstract

Utilization of health services by graduate students has been a neglected area of college health research. This paper describes the access problems and utilization patterns of a systematic random sample of the graduate student population at the University of Mississippi.

Survey methodology was used to assess sociodemographic, health status, and attitudinal characteristics of the study sample. In addition to type and number of visits for various health services, other utilization-related items included access to and satisfaction with care, and information received about these health services.

The results indicated that graduate students and their dependents were reliant to a large degree on local health care. Inadequacy of information was viewed as a major problem relating to access. Satisfaction with care appeared to be a function of the quality of care received.     

WHAT MAKES THE LOCAL? A BRIEF CONSIDERATION OF THE REJUVENATION OF HONG KONG IDENTITY

This paper ascertains what makes the local and why the local is important, in the context of change in Hong Kong due to the political transition to PRC sovereignty.In doing so, I hope to pose a modest polemical challenge to cultural studies' tendency to overlook seemingly simplistic empirical information. The return of Hong Kong to China in 1997 has led to a contraction of the political sphere, as the convergence of political structures curbed the development of local identities. The label or category ‘Hong Kong people’ was then appropriated with a specific meaning for the local to resist encroachment of the national. It was true that the high intensity of dominant national discourses during the political transition created a favourable atmosphere for re-nationalization. However, as soon as the political transition was over, Hong Kongers re-adhered to their own label in their struggle for cultural autonomy.Their strong cultural affect toward various national icons during the transition quickly diminished. This multiyear discourse study (1996–1998), which utilizes social scientific methods in conjunction with cultural theories, illustrates important political and methodological impulses necessary for the formulation of a socio-political approach to cultural studies within the Hong Kong context.