Approximating probability density functions in hybrid Bayesian networks with mixtures of truncated exponentials

Mixtures of truncated exponentials (MTE) potentials are an alternative to discretization and Monte Carlo methods for solving hybrid Bayesian networks. Any probability density function (PDF) can be approximated by an MTE potential, which can always be marginalized in closed form. This allows propagation to be done exactly using the Shenoy-Shafer architecture for computing marginals, with no restrictions on the construction of a join tree. This paper presents MTE potentials that approximate standard PDF’s and applications of these potentials for solving inference problems in hybrid Bayesian networks. These approximations will extend the types of inference problems that can be modelled with Bayesian networks, as demonstrated using three examples.     

Mental health, social relations, and social selection: a longitudinal analysis.

A wide body of literature documents the effect of social networks and social supports on mental health. Fewer studies, however, have examined the reciprocal effect of mental health on social relationships. This problem is examined using data from a national panel survey of adults aged 20-64. For the sample as a whole, support was found for a social selection process, since psychological distress predicted decreases in primary, but not secondary, social relationships. The extent of primary relationships also were found to be associated with subsequent distress, providing evidence that the relationship between mental health and social environment may be transactional. When examined separately by gender, males but not females were found to be vulnerable to the process of social selection, supporting the hypothesis that the expression of distress is less role-appropriate for men and therefore more likely to invite social sanctions. Social causation effects also were observed only among males.     

A hazard model of the probability of medical school drop-out in the UK

Summary.  From individual level longitudinal data for two entire cohorts of medical students in UK universities, we use multilevel models to analyse the probability that an individual student will drop out of medical school. We find that academic preparedness—both in terms of previous subjects studied and levels of attainment therein—is the major influence on withdrawal by medical students. Additionally, males and more mature students are more likely to withdraw than females or younger students respectively. We find evidence that the factors influencing the decision to transfer course differ from those affecting the decision to drop out for other reasons.     

Fields,networks and frames: advertising social organization in Japan

Abstract In this article I focus on three kinds of overlapping social coordinates — fields, networks and frames — as they are worked out in the day‐to‐day activities of a large Tokyo advertising agency. My aims are threefold. First, to show how the three social forms of fields, networks and frames interlock in a dialectical manner that permits both macro‐ and micro‐levels of sociological analysis. I thus present methodological approaches hitherto perceived to be different in emphases or interests as complementary rather than at odds with one another. Second, I take up and reexamine the notions of network and frame as developed within the specific context of Japanese social organization. Third, I make a statement in favour of anthropological studies of business as a means of understanding how industries and organizations function in a global economy.     

Easy-to-construct confidence bands for comparing two simple linear regression lines

This paper shows how to construct confidence bands for the difference between two simple linear regression lines. These confidence bands provide directly the information on the magnitude of the difference between the regression lines over an interval of interest and, as a by-product, can be used as a formal test of the difference between the two regression lines. Various different shapes of confidence bands are illustrated, and particular attention is paid towards confidence bands whose construction only involves critical points from standard distributions so that they are consequently easy to construct.     

Eye-Tracking Data: New Insights on Response Order Effects and Other Cognitive Shortcuts in Survey Responding

Survey researchers since Cannell have worried that respondents may take various shortcuts to reduce the effort needed to complete a survey. The evidence for such shortcuts is often indirect. For instance, preferences for earlier versus later response options have been interpreted as evidence that respondents do not read beyond the first few options. This is really only a hypothesis, however, that is not supported by direct evidence regarding the allocation of respondent attention. In the current study, we used a new method to more directly observe what respondents do and do not look at by recording their eye movements while they answered questions in a Web survey. The eye-tracking data indicate that respondents do in fact spend more time looking at the first few options in a list of response options than those at the end of the list; this helps explain their tendency to select the options presented first regardless of their content. In addition, the eye-tracking data reveal that respondents are reluctant to invest effort in reading definitions of survey concepts that are only a mouse click away or paying attention to initially hidden response options. It is clear from the eye-tracking data that some respondents are more prone to these and other cognitive shortcuts than others, providing relatively direct evidence for what had been suspected based on more conventional measures.     

Planning in a state of turbulence

This paper is concerned with an exploration of the role of the long range planner, whether in the private or public sector of the economy, and the impact made upon the processes of his work by government's increasing propensity to manipulate the economy. The authors' researches over the last 2 years into the comparative nature of planning processes in the U.K. economy have made it abundantly clear to them that planners are increasingly concerned at the dangerous potential of such impact upon their forecasting procedures. The emphasis here will rest upon the planner in private enterprises, although the authors' work in both local government and the nationalized enterprises suggest that the problem is of equal importance in these sectors.The authors consider first the past nature of the search processes in long range planning and the context of such attempts to narrow down the range of variables that form the enterprise's perception of its future. Secondly, they examine the emerging discontinuity and the changing role of government, with particular reference to indicative planning concepts. Then they introduce some of the findings of a recent survey of attitudes towards long range planning in the construction industry of the U.K., a sector vitally influenced by turbulence in the economy and with particular interest in government's ideas of macro-planning. Finally Edwards and Harris examine the implications to government and to planners of their findings.     

Improvement of Highway Safety I: Identification of Causal Factors Through Fault-Tree Modeling1

As the first article of a two-part series, the purpose of this paper is to examine the functional factors that contribute to automobile accident occurrence and to model the causation structure in the form of a fault-tree. The fault-tree model provides an intuitive framework for qualitatively decomposing possible pathways to accident occurrence. Fault-tree analysis also provides a statistical representation of how interacting driver, vehicle, and environmental factors contribute to the likelihood of automobile accident occurrence. The application of this model facilitates pinpointing those factors that most contribute to accident causation and subsequently enables the identification and comparison of potential crash avoidance technologies.     

Pseudo Self-Consistent Estimation of a Copula Model with Informative Censoring

Abstract.  We consider the case where a terminal event censors a non-terminal event, but not vice versa. When the events are dependent, estimation of the distribution of the non-terminal event is a competing risks problem, while estimation of the distribution of the terminal event is not. The dependence structure of the event times is formulated with the gamma frailty copula on the upper wedge, with the marginal distributions unspecified. With a consistent estimator of the association parameter, pseudo self-consistency equations are derived and adapted to the semiparametric model. Existence, uniform consistency and weak convergence of the new estimator for the marginal distribution of the non-terminal event is established using theories of empirical processes, U -statistics and Z -estimation. The potential practical utility of the methodology is illustrated with simulated and real data sets.