Jointly modeling time-to-event and longitudinal data: a Bayesian approach

This article explores Bayesian joint models of event times and longitudinal measures with an attempt to overcome departures from normality of the longitudinal response, measurement errors, and shortages of confidence in specifying a parametric time-to-event model. We allow the longitudinal response to have a skew distribution in the presence of measurement errors, and assume the time-to-event variable to have a nonparametric prior distribution. Posterior distributions of the parameters are attained simultaneously for inference based on Bayesian approach. An example from a recent AIDS clinical trial illustrates the methodology by jointly modeling the viral dynamics and the time to decrease in CD4/CD8 ratio in the presence of CD4 counts with measurement errors to compare potential models with various scenarios and different distribution specifications. The analysis outcome indicates that the time-varying CD4 covariate is closely related to the first-phase viral decay rate, but the time to CD4/CD8 decrease is not highly associated with either the two viral decay rates or the CD4 changing rate over time. These findings may provide some quantitative guidance to better understand the relationship of the virological and immunological responses to antiretroviral treatments.     

A continuous general multivariate distribution and its properties

Starting from two known continuous univariate distributions, a bivariate distribution is constructed depending on a parameter which measures the degree of stochastic dependence between the two random variables. From the foregoing construction we then pass to a multivariate-type distribution, constructed using only univariate distributions and an association matrix. Some properties of the multivariate and bivariate case are studied.     

MARKET DISTORTIONS AND GOVERNMENT TRANSPARENCY

In this paper, we investigate how government transparency depends on economic distortions. We first consider an abstract class of economies in which a benevolent policy maker is privately informed about the exogenous state of the economy and contemplates whether to release this information. Our key result is that distortions limit communication: even if transparency is ex ante Pareto superior to opaqueness, it cannot constitute an equilibrium when distortions are sufficiently high. We next confirm this broad insight in two applied contexts, in which monopoly power and income taxes are the specific sources of distortions.     

A Review of Multicomponent Interventions to Prevent and Control Tobacco Use Among College Students

Abstract

Objective: Multicomponent tobacco control programs have been implemented at the state and community levels and have led to a reduction in tobacco use. The purpose was to review the public health research literature on tobacco prevention and control programs on college campuses and derive evidence-based implications for comprehensive program implementation. Methods: MEDLINE, PsycINFO, ERIC, and PubMed databases were used to search the research literature concerning tobacco prevention and control programs conducted on college campuses published between 2000 and 2009. Results: No studies were found that implemented all 5 recommended components of a comprehensive program. Tobacco control programs containing policy and prevention education were used the most and promotion of tobacco-free environments and banning sales of tobacco products were used the least. Conclusion: The review suggests that despite the recommendation of comprehensive tobacco control programs to reduce tobacco use on college campuses, few institutions have implemented and evaluated programs consisting of multiple components.     

Combining Measures of Risk Perceptions and Risk Activities: The Development of the RAPRA and PRISC Indices

The influence of risk perceptions on risk activities of teenagers is well known, but the development of indices, which combine measures of perception as well as behavioral outcomes, has proved problematical. This article discusses the ways in which this methodological problem was tackled within a five-year, multiphase, multimethod study of factors affecting adolescent risk-taking in Tasmania, Australia, which included an intergenerational comparison of adolescents and parents. The development of the Risk Activity by Personal Risk Assessment (RAPRA) Index combines measures of perceived riskiness of 26 activities identified by young people as involving varying degrees of risk, with the degree of participation by each respondent, through a rectangular model of weights. The Personal Risk Score Category (PRISC) Index summarizes and categorizes an individual's risk-taking profile relative to the group's risk values and risk hierarchy established by the RAPRA Index. The article discusses ways in which technical problems involved in combining measures of risk perceptions and risk activities were addressed during index construction, compared with examples in the literature. Some key findings from analysis of two student and parent samples are presented as exemplars of the methods used and the results produced. Findings demonstrate the widespread nature of risk-taking among teenagers, and the similarity of levels of risk-taking between teenager and parental generations. The indices allow for detailed comparison of particular risk-taking activities and reveal differences among teenagers now compared with parents when they were teenagers, and illustrate the dynamic cultural context of risk-taking perceptions and values.     

Assessment Frameworks: A Critical Reflection

Increasing widespread requirements that assessment practiceconforms to generic guidelines contained in assessment frameworkshas been contentious and critiques offered on individual frameworkshave been assumed to apply to the concept of assessment frameworksmore generally. After comparing four assessment frameworks currentlybeing used in the UK, this paper argues that although some generalizationscan be made, for the most part, they are highly individual documentsin terms of range and depth of content, the extent to whichthey are evidenced and the quality of that evidence and implicitexpectations as to the skill bases of assessors. Furthermore,the introduction of assessment frameworks is not in itself apanacea to ensure good practice. Even with the most comprehensiveframeworks, social workers will still need comprehensive trainingin assessment and supervision of their practice.