Bayesian Analysis of Instrumental Variable Models: Acceptance-Rejection within Direct Monte Carlo

We discuss Bayesian inferential procedures within the family of instrumental variables regression models and focus on two issues: existence conditions for posterior moments of the parameters of interest under a flat prior and the potential of Direct Monte Carlo (DMC) approaches for efficient evaluation of such possibly highly non-elliptical posteriors. We show that, for the general case of m endogenous variables under a flat prior, posterior moments of order r exist for the coefficients reflecting the endogenous regressors’ effect on the dependent variable, if the number of instruments is greater than m +r, even though there is an issue of local non-identification that causes non-elliptical shapes of the posterior. This stresses the need for efficient Monte Carlo integration methods. We introduce an extension of DMC that incorporates an acceptance-rejection sampling step within DMC. This Acceptance-Rejection within Direct Monte Carlo (ARDMC) method has the attractive property that the generated random drawings are independent, which greatly helps the fast convergence of simulation results, and which facilitates the evaluation of the numerical accuracy. The speed of ARDMC can be easily further improved by making use of parallelized computation using multiple core machines or computer clusters. We note that ARDMC is an analogue to the well-known “Metropolis-Hastings within Gibbs” sampling in the sense that one ‘more difficult’ step is used within an ‘easier’ simulation method. We compare the ARDMC approach with the Gibbs sampler using simulated data and two empirical data sets, involving the settler mortality instrument of Acemoglu et al. (2001 Acemoglu , D. , Johnson , S. , Robinson , J. A. ( 2001 ). The colonial origins of comparative development: An empirical investigation . American Economic Review 91 ( 5 ): 1369 – 1401 .[Crossref], [Web of Science ®] , [Google Scholar]) and father's education's instrument used by Hoogerheide et al. (2012a Hoogerheide , L. F. , Block , J. H. , Thurik , A. R. (2012a). Family background variables as instruments for education in income regressions: A Bayesian analysis. Economics of Education Review 31(5):515–523.[Crossref], [Web of Science ®] , [Google Scholar]). Even without making use of parallelized computation, an efficiency gain is observed both under strong and weak instruments, where the gain can be enormous in the latter case.     

Combined Density Nowcasting in an Uncertain Economic Environment

We introduce a combined density nowcasting (CDN) approach to dynamic factor models (DFM) that in a coherent way accounts for time-varying uncertainty of several model and data features to provide more accurate and complete density nowcasts. The combination weights are latent random variables that depend on past nowcasting performance and other learning mechanisms. The combined density scheme is incorporated in a Bayesian sequential Monte Carlo method which rebalances the set of nowcasted densities in each period using updated information on the time-varying weights. Experiments with simulated data show that CDN works particularly well in a situation of early data releases with relatively large data uncertainty and model incompleteness. Empirical results, based on U.S. real-time data of 120 monthly variables, indicate that CDN gives more accurate density nowcasts of U.S. GDP growth than a model selection strategy and other combination strategies throughout the quarter with relatively large gains for the two first months of the quarter. CDN also provides informative signals on model incompleteness during recent recessions. Focusing on the tails, CDN delivers probabilities of negative growth, that provide good signals for calling recessions and ending economic slumps in real time.     

The 1991–2004 Evolution in Life Expectancy by Educational Level in Belgium Based on Linked Census and Population Register Data

The aim of this study is to determine trends in life expectancy by educational level in Belgium and to present elements of interpretation for the observed evolution. The analysis is based on census data providing information on educational level linked to register data on mortality for the periods 1991–1994 and 2001–2004. Using exhaustive individual linked data allows to avoid selection bias and numerator–denominator bias. The trends reveal a general increase in life expectancy together with a widening social gap. Summary indices of inequality based on life expectancies show, however, a more complex pattern and point to the importance to include the shifts in population composition by educational level in an overall assessment of the evolution of inequality by educational level.     

Missing data: Discussion points from the PSI missing data expert group

The Points to Consider Document on Missing Data was adopted by the Committee of Health and Medicinal Products (CHMP) in December 2001. In September 2007 the CHMP issued a recommendation to review the document, with particular emphasis on summarizing and critically appraising the pattern of drop‐outs, explaining the role and limitations of the ‘last observation carried forward’ method and describing the CHMP's cautionary stance on the use of mixed models. In preparation for the release of the updated guidance document, statisticians in the Pharmaceutical Industry held a one‐day expert group meeting in September 2008. Topics that were debated included minimizing the extent of missing data and understanding the missing data mechanism, defining the principles for handling missing data and understanding the assumptions underlying different analysis methods. A clear message from the meeting was that at present, biostatisticians tend only to react to missing data. Limited pro‐active planning is undertaken when designing clinical trials. Missing data mechanisms for a trial need to be considered during the planning phase and the impact on the objectives assessed. Another area for improvement is in the understanding of the pattern of missing data observed during a trial and thus the missing data mechanism via the plotting of data; for example, use of Kaplan–Meier curves looking at time to withdrawal. Copyright © 2009 John Wiley & Sons, Ltd.     

Introduction to the Special Issue on Theory Development in Operations Management

Rigorous development of theory in operations management has been lacking. Although many theories have been proposed, they are often not developed in a format and depth that can be falsified, refined, or supported. This special issue includes three papers that illustrate rigorous development of theory for future testing using mathematical, simulation, or managerial approaches.     

Ping‐pong poms: emotional reflexivity in contemporary return migration from Australia to the United Kingdom

About 20,000 people from the United Kingdom emigrate to Australia each year. Of these, a significant number return to the United Kingdom, and some return again to Australia. Studies of such patterns of migration and return (and return again) were quite common a few decades ago, but are now rare. This paper makes use of a contemporary data source – an Internet‐mediated discussion forum – to explore the experiences of modern ‘ping‐pong poms’. A picture emerges of these migrants as exercising emotional reflexivity in dealing with the pull of family left behind, ‘homesickness’, the lack of a sense of belonging and their often‐disappointed dreams of a ‘better life’. By understanding the importance of emotions in people's decisions about return migration, policy can better attend to the realities of more mobile lives.     

The Sex Check: The Development of an HIV-Prevention Service to Address the Needs of Latino MSM

The Sex Check is a brief, telephone-delivered, HIV-prevention intervention tailored for individuals who are at high risk of HIV infection or transmission but who are neither reducing their risk on their own nor seeking support for this purpose. Because the intervention is delivered on a one-to-one basis, permits anonymity, is marketed to "men who have sex with men," and is brief, it may be particularly responsive to cultural, structural, and attitudinal barriers to serving Latino MSM. Because many Latino MSM continue to engage in high risk sexual behaviors, developing and testing prevention interventions with this population is a public health priority.     

The roles and rules of law in sexual development

This article provides an overview of the diverse sources of law that regulate sexual development and its resulting behaviors, dispositions, and outcomes. After exploring how the law influences sexuality by regulating families, schools, media, and social service delivery, the article examines the role of criminal and civil law in regulating partners influences on sexual relationships. The article then briefly analyses how the law influences the manner individuals themselves influence their intimate relationships and social environments. The article emphasizes that the necessary brevity of the overview masks many complexities but that existing laws and trends highlight how the law plays a dominant role in our lives, how the law seeks to promote certain dispositions, that the law must be harnessed to foster healthy relationships, and that contending with the law s dictates provides social scientists with important opportunities to foster social reform and structure healthy, supportive social environments conducive to responsible behaviors, attitudes, and dispositions.