Overfitting Bayesian Mixture Models with an Unknown Number of Components

This paper proposes solutions to three issues pertaining to the estimation of finite mixture models with an unknown number of components: the non-identifiability induced by overfitting the number of components, the mixing limitations of standard Markov Chain Monte Carlo (MCMC) sampling techniques, and the related label switching problem. An overfitting approach is used to estimate the number of components in a finite mixture model via a Zmix algorithm. Zmix provides a bridge between multidimensional samplers and test based estimation methods, whereby priors are chosen to encourage extra groups to have weights approaching zero. MCMC sampling is made possible by the implementation of prior parallel tempering, an extension of parallel tempering. Zmix can accurately estimate the number of components, posterior parameter estimates and allocation probabilities given a sufficiently large sample size. The results will reflect uncertainty in the final model and will report the range of possible candidate models and their respective estimated probabilities from a single run. Label switching is resolved with a computationally light-weight method, Zswitch, developed for overfitted mixtures by exploiting the intuitiveness of allocation-based relabelling algorithms and the precision of label-invariant loss functions. Four simulation studies are included to illustrate Zmix and Zswitch, as well as three case studies from the literature. All methods are available as part of the R package Zmix, which can currently be applied to univariate Gaussian mixture model

Barriers to Museums’ Informal Efforts to Facilitate Public Engagement with Science

This project embodies the author’s response to Alan Irwin’s essay (2014) calling for social scientists to “exercise greater imagination in helping foster a culture of experimentation in citizens’ responses to scientific fact and policy, thus acting to pluralize practice and offer ways of thinking that embrace different levels and ways of knowing”. In particular, this research focuses on museums as sites of public engagement with science through their participatory curricula. The author believes such curricula hold potential for building lay leadership skills by educating members of the public to employ mechanisms necessary to facilitate a type of deliberative democracy, giving birth to engagement as applied to science issues and policies. These necessary mechanisms, as listed by Ryfe (2005, 2006), comprise rules, stories, leadership, stakes, and apprenticeship

Influence of Involvement, Institutional Affiliation, and Geographic Location on Membership Retention in Voluntary Professional Organizations

The reasons people join voluntary professional organizations and continue membership is largely an unexplored area of research. This study sought to find some answers in membership data from the Association for Communication Excellence in Agriculture, Natural Resources, and Life and Human Sciences (ACE) from 1991 to 2004. Descriptive statistics, bivariate correlations, and, in some cases, simple linear regression were calculated for a variety of variables for 1,441 valid records. The findings suggest that a relationship exists between organization involvement and members’ identification with and sense of commitment to ACE, leading to continued membership. Findings also suggest that geography makes no difference in member retention. Results were unclear concerning the impact of employer affiliation on continued membership. Further research into individual member characteristics and the collection of more data are recommended

Impact of Newspaper Characteristics on Reporters\u27 Agricultural Crisis Stories: Productivity, Story Length, and Source Selection

This study examined coverage of the December 2003 bovine spongiform encephalopathy (BSE) event to discover differences in sources used by reporters based on their employing newspapers’ geographical location, circulation and ownership type. Sixty-two stories dealing with the first U.S. bovine spongiform encephalopathy incident were subjected to content analysis. Stories – published from December 23, 2003 to October 31, 2004 -- were selected through a keyword search from U.S. newspapers included in the LexisNexis database. These stories were divided into two equal groups based on reporters’ work-role identity and were analyzed by length, number of sources, and source variety and the employing newspapers’ geographical location, circulation and ownership type. ANOVA and bivariate correlation were among statistical analysis techniques used

Impact of Reporter Work Role Identity on News Story Source Selection: Implications for Coverage of Agricultural Crises

This study examined coverage of the December 2003 bovine spongiform encephalopathy (BSE) event to discover impact of reporters’ work role identities on news story source choices and to explore implications of results for agricultural crisis coverage. Content analysis was performed on 62 stories from U.S. newspapers in the Lexis Nexis database, selected through keyword search December 23, 2003 through October 31, 2004. These stories were divided into two equal groups based on reporters’ work-role identity (dichotomized between science-specialty beat reporters and non-specialty reporters) and analyzed by length, number of sources, and source variety. ANOVA and bivariate correlation statistics were used. Results indicated no statistically significant differences in mean story length or mean number of sources for stories written by science-specialty beat reporters and those written by non-specialty reporters. However, while mean overall source variety did not differ between the two reporter groups, work-role identify correlated with use of scientists and agricultural scientists as sources: science-specialty beat reporters used more such sources than did non-specialty reporters. Although this study was limited by small sample size and restriction to the first U.S. BSE event, the above findings may prove useful to agricultural public information officers and media relations practitioners in “pitching” stories and sources for similar agriculture-based crises. In particular, this study addresses priorities stated in the National Research Agenda - the desire of agricultural communicators to “aid the public in effectively participating in decision-making related to agriculture,” through providing information on which such decisions can be based (RPA2, 2007-2010, p. 4)

Institutional Transformation as Scholarly Activity: The Experience of Portland State University

In American higher education, change is continuous but occurs most often at the margins, generally taking the form of piecemeal or isolated efforts and programs. Only rarely are change projects comprehensive in their scope and transformative in their effects. In this chapter we describe the context for comprehensive curricular change at Portland State University and offer a more general theoretical construct about institutional change in higher education. That there are so few examples of comprehensive institutional change in American higher education is indicative of the complex mix of internal and external factors that constrain change efforts. We have found that while external factors provide an array of supportive and threatening messages, internal conditions determine whether the institution will choose to respond by creating an environment supportive of comprehensive change. From the Portland State experience we identify and discuss several factors which contributed to our decision to approach institutional reform in a comprehensive manner. A hallmark of the Portland State approach is that institutional reform is understood to be a scholarly activity, not administrative work. As we progressed through the change process we have identified three sets of scholarly questions which guide our work. These have followed each other in a generation sequence as the institution has moved through the stages of change. Our discussion of these points to the interplay between the process of change and building a scholarly basis to inform that process