A mixture of experts latent position cluster model for social network data

Social network data represent the interactions between a group of social actors. Interactions between colleagues and friendship networks are typical examples of such data.The latent space model for social network data locates each actor in a network in a latent (social) space and models the probability of an interaction between two actors as a function of their locations. The latent position cluster model extends the latent space model to deal with network data in which clusters of actors exist — actor locations are drawn from a finite mixture model, each component of which represents a cluster of actors.A mixture of experts model builds on the structure of a mixture model by taking account of both observations and associated covariates when modeling a heterogeneous population. Herein, a mixture of experts extension of the latent position cluster model is developed. The mixture of experts framework allows covariates to enter the latent position cluster model in a number of ways, yielding different model interpretations.Estimates of the model parameters are derived in a Bayesian framework using a Markov Chain Monte Carlo algorithm. The algorithm is generally computationally expensive — surrogate proposal distributions which shadow the target distributions are derived, reducing the computational burden.The methodology is demonstrated through an illustrative example detailing relationships between a group of lawyers in the USA.     

Improving OpenURL Menus: User Testing of Revisions to SFX® Menus

Abstract

Twenty-one volunteers tested the usability of revisions to the Texas A&M University Libraries' SFX® OpenURL link resolver menus, including the addition of Ex Libris' new bXâ?¢ recommendation service and a plug-in which pulls additional information about the journal into the menu. The volunteers also evaluated the quality and desirability of the bX recommendations and discussed their preferences for help options and full-text format. Results of the usability testing are reported along with the resultant menu changes. This study will be of interest to librarians implementing or redesigning OpenURL menus as well as those interested in the user experience.     

Race-Related Correlates of Young Adults' Subjective Well-Being

We investigated how often young adults worry about race relationsand whether they perceive that white/black relations have beendeteriorating. We also explored the relationships betweenrace-related worry and pessimism, and subjective well-being. This study addressed the distribution of race-related worry andpessimism, and their relationship to subjective well-being innational probability samples of high school seniors completingself-administered questionnaires in 1996 and 1997 (n = 4,514). Nearly one-third of high school seniors often worry about racerelations, and about 20% perceive that contemporary white/blackrelations have been getting at least a little worse. Worryingoften about race relations and perceiving that race relationshave been getting worse were significantly associated withdiminished levels of life satisfaction and happiness. Theresults confirm that race-related worry and pessimism werecommon, and that they impact youth's affective and cognitivestates.     

The effects of family caps on the subsequent fertility decisions of never-married mothers

Family caps seek to reduce fertility among welfare recipients by denying additional cash assistance to recipients who have children while on welfare. A necessary condition for family caps to be an effective policy tool is that welfare recipients respond to financial incentives in making decisions that affect subsequent fertility outcomes. This paper uses data from the 2001 and 2004 panels of the Survey of Income and Program Participation (SIPP) to examine whether welfare mothers respond to the incentive provided by the Aid to Families with Dependent Children/Temporary Assistance to Needy Families (AFDC/TANF) system in determining whether or not to have a second child. The results show no evidence that family caps have an effect on the subsequent childbearing of never married women.

Lavender Islands: the New Zealand study

Lavender Islands: Portrait of the Whole Family is the first national strengths-based study of lesbian, gay, and bisexual (LGB) people in New Zealand. The 133-item survey was made available both by website and paper copy from April to July 2004. Multidisciplinary interest areas were developed by a community reference group, and included identity and self-definition, families of origin, relationships and sexuality, families of choice, immigration and internal migration, wellbeing, politics, income and spending, education, careers and leisure, community connections, challenges, and spirituality. A four-axis model of sexual identity was also tested; 2,269 responses were received. Of these 83% were from the website; 45% of responses were from women and 54% from men. Responses identified a robust, highly educated, relatively high-income, politically active LGB community. Male and female respondents experienced same-sex relationships and identity in significantly different ways.     

Factors associated with long-term benzodiazepine use among elderly women and men in Quebec

The goal of this study was to compare factors associated with long-term benzodiazepine use by elderly women and men (n = 1701) who participated in the Quebec Health Survey (QHS). Data from the 1998 QHS were linked with data from the administrative files of the Régie de l'assurance maladie du Québec. Results showed that elderly women were more at risk than men for long-term benzodiazepine use. Results of the multivariate logistic regression did not show a significant difference between women and men on any of the risk factors studied. Other factors such as elderly and physician attitudes deserve further study to explain differences in long-term benzodiazepine use between elderly women and men.