Series evaluation of Tweedie exponential dispersion model densities

Exponential dispersion models, which are linear exponential families with a dispersion parameter, are the prototype response distributions for generalized linear models. The Tweedie family comprises those exponential dispersion models with power mean-variance relationships. The normal, Poisson, gamma and inverse Gaussian distributions belong to theTweedie family. Apart from these special cases, Tweedie distributions do not have density functions which can be written in closed form. Instead, the densities can be represented as infinite summations derived from series expansions. This article describes how the series expansions can be summed in an numerically efficient fashion. The usefulness of the approach is demonstrated, but full machine accuracy is shown not to be obtainable using the series expansion method for all parameter values. Derivatives of the density with respect to the dispersion parameter are also derived to facilitate maximum likelihood estimation. The methods are demonstrated on two data examples and compared with with Box-Cox transformations and extended quasi-likelihoood.     

Evidence for attitudinal-behavioural consistency: Implications for consumer research paradigms

Evidence is presented in this paper to show that the view of marketing communication effects promulgated by numerous marketing, advertising and consumer behaviour texts and journals should be questioned. This is the portraval of advertising, in particular, as strongly persuasive, a prepurchase influence which acts upon purchase behaviour by first operating upon and modifying mental attitudes. The latent process conception of attitude upon which this perspective is founded lacks convincing empirical support. Situational rather than inner-state variables appear to mediate behaviour and may require prior importance in explicative and predictive accounts of consumer choice. Recognition of this would require a probability conception of the attitude construct which would have profound implications for consumer research and marketing management. Above all, it suggests that an alternative psychological paradigm might he accorded a more central place in investigations of consumer behaviour.     

Measuring safety climate on offshore installations

The human and organizational factors affecting safety were examined on 10 offshore installations using the Offshore Safety Questionnaire. The questionnaire contained scales measuring work pressure and work clarity, job communication, safety behaviour, risk perception, satisfaction with safety measures and safety attitudes. A total of 722 UK offshore workers (33% response rate) from a range of occupations completed and returned the questionnaire. The 'safety climates' on the various installations were characterized by most respondents feeling 'safe' with respect to a range of offshore hazards and expressing 'satisfaction' with safety measures. Respondents reported little risk-taking behaviour and felt positive about levels of work clarity and job communication. There was a wider diversity of opinions on the safety attitudes scale, indicating a lack of a positive, concerted 'safety culture' and more evidence for a range offragmented 'safety subcultures', which varied mainly as a function of seniority, occupation, age, shift worked and prior accident involvement. It is suggested that the interaction between these differing subcultures partly determines the prevailing 'safety climate' on any given installation. The UK oil and gas industry is now trying to improve its safety culture through the 'Stepchange' initiative, which hias set itself three main targets for the year 2000 : a 50 YO improvement in the industry's safety performance; safety performance contracts demonstrating leadership's personal concern for safety as an equal to business performance and encouraging industry members to work together to improve sharing of safety information and good practice. It is suggested that the existence of a strong, cohesive culture with respect to safety is not necessarily beneficial, possibly leading to 'dry rot' and complacency. A healthy culture may be represented by a range of assumptions, values, norms and expectations as reflected in employees' differing experiences of safety climate.     

The roots,significance, value and legislation of gambling

In this highly personal account, Reverend Moody traces his exploration for over three decades of many facets of the underlying nature of gambling in society and in human nature. He makes the case that much of the appeal of gambling comes from the excitement of playing with chance, and discusses how different types of gambling — lotteries, wagering, and continuous betting — meet a variety of needs and pose diverse levels of risk to gamblers. He notes distinctions between controlled and uncontrolled gamblers, and the tendency for controlled gamblers to play on the edge and risk loss of control. He notes difficulties in preventing the excesses that can occur to individuals who gamble. He points out the problems with legislatures legalizing gambling for ulterior purposes, such as to raise tax revenue, rather than to cater to the demand for gambling from punters. This can lead to situations where commercial gaming interests are not directed to act in the best interests of the general public because potential problems that may arise with available gambling are ignored or deemphasized. Finally, he points out the tensions amongst various interest groups who deal with gambling and notes those forums which have evolved in recent years that provide greater opportunities for dialogue among the various entities who deal with gambling and public policy issues.Gordon Moody was ordained a Minister of the Methodist Church in 1942. In recognition of his work on gambling, he was awarded the M.B.E. (Member of the Most Excellent Order of the British Empire) by the Queen in 1969. In 1980, the Open University conferred on him the Honorary Degree of Master of Arts. (See obituary, pp. 3–7). This issue is dedicated to his memory.     

A Common Rationale for Global Sensitivity Measures and Their Estimation

Measures of sensitivity and uncertainty have become an integral part of risk analysis. Many such measures have a conditional probabilistic structure, for which a straightforward Monte Carlo estimation procedure has a double‐loop form. Recently, a more efficient single‐loop procedure has been introduced, and consistency of this procedure has been demonstrated separately for particular measures, such as those based on variance, density, and information value. In this work, we give a unified proof of single‐loop consistency that applies to any measure satisfying a common rationale. This proof is not only more general but invokes less restrictive assumptions than heretofore in the literature, allowing for the presence of correlations among model inputs and of categorical variables. We examine numerical convergence of such an estimator under a variety of sensitivity measures. We also examine its application to a published medical case study.     

‘We can’t let them fail for one more day’: School reform urgency and the politics of reformer-community alliances

This article provides a critical examination of neoliberal urgency in education reform. While critics of neoliberal reform policies have argued that these reforms exclude low-income community participation almost entirely, I argue that in practice this exclusion is not as total or as overt as macro-analyses would suggest. These macro analyses do not explain the complicated alliances that reformers have with some community organizations, nor do they specifically and critically examine the role that urgency plays in determining the value of community voice in school reform decisions. On the ground, elite school reformers forge tenuous alliances with select low-income community groups, while disregarding and marginalizing others. In this article, I posit that ‘urgency,’ a cherished ideal and guiding principle of the neoliberal school reform movement, becomes the mechanism for elite school reformers to distinguish ‘good’ and valuable community allies from ‘backwards’ and ignorant community voices. A critical examination of school reformer narratives in particular reveals that the discourse and practice of school reform urgency both legitimizes and hides a more profound exclusion of low-income African American voices from the school reform process.     

Uncertainties in Biologically-Based Modeling of Formaldehyde-Induced Respiratory Cancer Risk: Identification of Key Issues

In a series of articles and a health-risk assessment report, scientists at the CIIT Hamner Institutes developed a model (CIIT model) for estimating respiratory cancer risk due to inhaled formaldehyde within a conceptual framework incorporating extensive mechanistic information and advanced computational methods at the toxicokinetic and toxicodynamic levels. Several regulatory bodies have utilized predictions from this model; on the other hand, upon detailed evaluation the California EPA has decided against doing so. In this article, we study the CIIT model to identify key biological and statistical uncertainties that need careful evaluation if such two-stage clonal expansion models are to be used for extrapolation of cancer risk from animal bioassays to human exposure. Broadly, these issues pertain to the use and interpretation of experimental labeling index and tumor data, the evaluation and biological interpretation of estimated parameters, and uncertainties in model specification, in particular that of initiated cells. We also identify key uncertainties in the scale-up of the CIIT model to humans, focusing on assumptions underlying model parameters for cell replication rates and formaldehyde-induced mutation. We discuss uncertainties in identifying parameter values in the model used to estimate and extrapolate DNA protein cross-link levels. The authors of the CIIT modeling endeavor characterized their human risk estimates as "conservative in the face of modeling uncertainties." The uncertainties discussed in this article indicate that such a claim is premature.     

Understanding and (dis)trusting food assurance schemes: Consumer confidence and the ‘knowledge fix’

This paper uses evidence from focus groups with consumers in England to consider how consumers understand and evaluate a range of proxies or intermediary organisations that offer assurance about food and consumer products, particularly voluntary certification schemes. This addresses the current concern in developed economies about providing information in order to reconnect consumers with food producers and to support moves towards more local, fairly traded and sustainable production. However, we show that such a ‘knowledge fix’ approach of providing information may not reconnect consumers so easily. Participants found it particularly difficult to work out what certification involved and what kinds of organisations were providing assurance. They built vernacular typologies and comparative judgements that did not necessarily identify or prioritise ‘independent’ third-party certification as the gold standard, not least because of the practical difficulties of monitoring complex supply chains, and expressed confusion and scepticism about how well food assurance schemes could work in practice. Our results therefore problematise the knowledge fix urged in the literature and emphasise instead the need to better understand how consumers make sense of assurance information in different contexts.