Improved estimators for the shape parameter in gamma regression

A regression model is considered in which the response variables have gamma distributions with a common shape parameter. A review is given of existing estimators for the shape parameter. Bias expressions for the maximum likelihood estimates of the regression coe f f i c i ent s and the shape parameter are developed. A new estima t o r f o r t h e shape parameter based on bias correction for the maximum likelihood estimator is shown to have markedly better variance and mean square error properties in small to moderate sized samples. Approximations to the low order moments of the Pearson statistic are derived for gamma regression models with general link functions. These are used for the case of a logarithmic link to develop new estimators for the shape parameter which have better moment properties than the estimators based on the Pearson statistic which have been used previously. Finally, the small sample variance and mean square error efficiencies of the estimators relative to the maximum likelihood estimator are evaluated by simulation for the case of a single explanatory variable and a logarithmic link, for a range of sample sizes less than or equal to 100

Secrets of Success: Identifying Success Factors in Institutional Repositories

4th International Conference on Open RepositoriesThis presentation was part of the session : Conference PresentationsDate: 2009-05-19 08:30 AM – 09:30 AMThere is little agreement on which factors lead to successful institutional repositories. Researchers primarily cite content recruitment and services as key factors; however, there has also been discussion of measuring IR success in terms of how well the IR furthers the overall goals of the library. This paper examines the topic of IRs and success. Our findings are based on a comparative case study of five IRs in colleges and universities. We argue that success should be measured by both internal (e.g., content or services) as well as external factors - how well the IR fulfills or brings the library closer to achieving its long-term goals in terms of service to the academic community.Institute of Museum and Library Service

Phase transition of the susceptible-infected-susceptible dynamics on time-varying configuration model networks

We present a degree-based theoretical framework to study the susceptible-infected-susceptible (SIS) dynamics on time-varying (rewired) configuration model networks. Using this framework, we provide a detailed analysis of the stationary state that covers, for a given structure, every dynamic regimes easily tuned by the rewiring rate. This analysis is suitable for the characterization of the phase transition and leads to three main contributions. (i) We obtain a self-consistent expression for the absorbing-state threshold, able to capture both collective and hub activation. (ii) We recover the predictions of a number of existing approaches as limiting cases of our analysis, providing thereby a unifying point of view for the SIS dynamics on random networks. (iii) We reinterpret the concept of hub-dominated phase transition. Within our framework, it appears as a heterogeneous critical phenomenon : observables for different degree classes have a different scaling with the infection rate. This leads to the successive activation of the degree classes beyond the epidemic threshold.Comment: 14 pages, 11 figure

Ultimate strength equation for pultruded CFRP plates in fire

The paper presents a model for the ultimate strength calculation of fibre-reinforced polymer (FRP) pultruded plates in fire. The model is calibrated from a series of coupon tests on pultruded CFRP plates carried out using steady state and transient state test methods. In the steady state tests, temperatures ranging from ambient to approximately 700℃ were considered. The test specimens were heated to a specified temperature then loaded until failure while the same temperature was maintained throughout the test. Different periods of times of 5 and 30 minutes were maintained to investigate the effect of heating duration. In the transient state tests, the test specimens were loaded to a specified stress level prior to heating, and then the temperature was increased until failure of the test specimens. Three different stress levels applied to the pultruded CFRP plates were considered. Based on the test results, an ultimate strength equation is proposed which has been inspired from a model developed for metallic materials subjected to elevated temperatures. Application of the model is finally demonstrated in a worked example.postprin

Effect of surface preparation on the strength of FRP-to-mild steel and FRP-to-stainless steel joints

A detailed understanding of the strength and behaviour of the bond between fibre-reinforced polymer (FRP) composites to metals is an ongoing field of research. The many different geometrical and ma-terial parameters make for extensive research demands. This paper in turn reports a series of tests on the shear strength and behaviour of FRP-to metal joints in which the main test parameters, which have received limited attention to date, consists of (i) type of metal (i.e. non-galvanised mild steel and stainless steel), and (ii) sur-face preparation technique (i.e. different mechanical abrasion methods). All specimens are loaded in dis-placement control which enables the failure process to be followed and identification of different failure modes to be made. The results enable the effectiveness of different surface preparation techniques upon the bond of FRP to different types of metals to be made.postprintThe 5th International Conference on FRP Composites in Civil Engineering (CICE 2010), Beijing, China, 27-29 September 2010. In proceedings of the 5th CICE, 2010, p. 869-87

La validité en tant qu’impératif social : perceptions d’utilisateurs et de leaders

Introduction: Recently, validity as a social imperative was proposed as an emerging conceptualization of validity in the assessment literature in health professions education (HPE). To further develop our understanding, we explored the perceived acceptability and anticipated feasibility of validity as a social imperative with users and leaders engaged with assessment in HPE in Canada. Methods: We conducted a qualitative interpretive description study. Purposeful and snowball sampling were used to recruit participants for semi-structured individual interviews and focus groups. Each transcript was analyzed by two team members and discussed with the team until consensus was reached. Results: We conducted five focus group and eleven interviews with two different stakeholder groups (users and leaders). Our findings suggest that the participants perceived the concept of validity as a social imperative as acceptable. Regardless of group, participants shared similar considerations regarding: the limits of traditional validity models, the concept’s timeliness and relevance, the need to clarify some terms used to characterize the concept, the similarities with modern theories of validity, and the anticipated challenges in applying the concept in practice. In addition, participants discussed some limits with current approaches to validity in the context of workplace-based and programmatic assessment. Conclusion: Validity as a social imperative can be interwoven throughout existing theories of validity and may represent how HPE is adapting traditional models of validity in order to respond to the complexity of assessment in HPE; however, challenges likely remain in operationalizing the concept prior to its implementation.Contexte : Une nouvelle manière de concevoir la validité en matière d’évaluation des apprentissages dans les programmes en sciences de la santé a récemment été proposée : la validité en tant qu’impératif social. Pour mieux la comprendre, nous avons exploré l’acceptabilité perçue et la faisabilité anticipée de la validité en tant qu’impératif social auprès d’utilisateurs et de leaders en matière d’évaluation en éducation des professions de la santé au Canada. Méthodes : Nous avons mené une étude qualitative descriptive interprétative. Pour recruter les participants aux entrevues individuelles semi-structurées et aux groupes de discussion, nous avons utilisé l’échantillonnage par choix raisonné et l’échantillonnage boule de neige. Les transcriptions ont été analysées par deux membres de l’équipe et discutées avec l’ensemble de l’équipe jusqu’à l’obtention d’un consensus. Résultats : Nous avons mené cinq groupes de discussion et onze entretiens avec deux groupes de parties prenantes, l’un composé d’utilisateurs, l’autre de leaders. Nos résultats suggèrent que les participants estiment acceptable le concept de validité comme impératif social. Quel que soit le groupe, les participants ont partagé des considérations similaires concernant : les limites des modèles de validité traditionnels, l’actualité et la pertinence du concept, la nécessité de clarifier certains termes utilisés pour définir le concept, les similitudes avec les théories modernes de la validité, et les défis anticipés de son application. En outre, les participants ont soulevé certaines limites des approches actuelles de la validité dans le contexte de l’évaluation en milieu de travail et de l’évaluation programmatique. Conclusion : La notion de validité comme impératif social peut être incorporée dans les théories existantes pour traduire l’adaptation des modèles traditionnels de la validité à la complexité de l’évaluation en éducation des professions de la santé; cependant, certains défis liés à l’opérationnalisation du concept seraient à résoudre avant sa mise en œuvre

Universality of the stochastic block model

Mesoscopic pattern extraction (MPE) is the problem of finding a partition of the nodes of a complex network that maximizes some objective function. Many well-known network inference problems fall in this category, including, for instance, community detection, core-periphery identification, and imperfect graph coloring. In this paper, we show that the most popular algorithms designed to solve MPE problems can in fact be understood as special cases of the maximum likelihood formulation of the stochastic block model (SBM), or one of its direct generalizations. These equivalence relations show that the SBM is nearly universal with respect to MPE problems.Comment: 13 pages, 4 figure