1,720,985 research outputs found
Editorial: Multivariate Probabilistic Modelling for Risk and Decision Analysis
No full textApplied Probabilit
Multivariate Methods for Coastal and Offshore Risks
No full textThis thesis investigates how selected multivariate probabilistic methods can be adapted for risk analysis and decision making in coastal and offshore environments. In particular, the thesis makes a contribution to decision support tools for risk reduction efforts in coastal environments and to statistical simulation methods for wave conditions. Generally, very few observations on negative impacts in coastal or offshore environments are available for risk analysis or decision making due to the rare nature of extreme events. However, synthetic impact data can be generated by propagating relevant hydro meteorological conditions to the environment of interest through a chain of multiple models. Especially in coastal environments, this chain often includes computationally intensive models.Coastal Engineerin
Levee system reliability modeling: The length effect and Bayesian updating
No full textIn levee system reliability, the length effect is the term given to the phenomenon that the longer the levee, the higher the probability that it will have a weak spot and fail. Quantitatively, it is the ratio of the segment failure probability to the cross-sectional failure probability. The literature is lacking in methods to calculate the length effect in levees, and often over-simplified methods are used. An efficient (but approximate) method, which we refer to as the modified outcrossing (MO) method, was developed for the system reliability model used in Dutch national flood risk analysis and for the provision of levee assessment tools, but it is poorly documented and its accuracy has not been tested. In this paper, we propose a method to calculate the length effect in levees by sampling the joint spatial distribution of the resistance variables using a copula approach, and represented by a Bayesian Network (BN). We use the BN to verify the MO method, which is also described in detail in this paper. We describe how both methods can be used to update failure probabilities of (long) levees using survival observations (i.e., high water levels and no levee failure), which is important because we have such observations in abundance. We compared the methods via a numerical example, and found that the agreement between the segment failure probability estimates was nearly perfect in the prior case, and very good in the posterior case, for segments ranging from 500 m to 6000 m in length. These results provide a strong verification of both methods, either of which provide an attractive alternative to the more simplified approaches often encountered in the literature and in practice.Hydraulic Structures and Flood RiskDynamics of Structure
Recent Advances in the Elicitation of Uncertainty Distributions from Experts for Multinomial Probabilities
No full textIn this chapter, we consider the problem of the elicitation and specification of an uncertainty distribution based on expert judgements, which may be a subjective prior distribution in a Bayesian analysis, for a set of probabilities which are constrained to sum to one. A typical context for this is as a prior distribution for the probabilities in a multinomial model. The Dirichlet distribution has long been advocated as a natural way to represent the uncertainty distribution over the probabilities in this context. The relatively small number of parameters allows for specification based on relatively few elicited quantities but at the expense of a very restrictive structure. We detail recent advances in elicitation for the Dirichlet distribution and recently proposed alternative approaches, which offer greater flexibility at the expense of added complexity. In order of increasing flexibility, they are the generalised Dirichlet distribution, multivariate copulas and vines. An extension of multinomial models containing covariates is discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Structured expert judgement for decisions on medicines policy and management
No full textMany decisions related to the marketing authorisation of medicinal products as well as decisions for processes such as Health Technology Assessment (HTA), reimbursement and pricing of medicines, and the setting of clinical guidelines, are taken in the face of significant uncertainties. Moreover, decision making can be impacted by biases resulting from psychological heuristics. In other domains where decisions have to be taken with imperfect or incomplete evidence, Structured Expert Judgement (SEJ) has been found to be useful in making the best use of available evidence, and synthesising it with professional expertise, stakeholders’ values and concerns. To date, formal SEJ has only been used to a limited extent in healthcare. Aspects affecting decisions for marketing authorisation and health technology assessment, reimbursement and pricing of medicines are described and the main risks and uncertainties are identified. Some considerations and recommendations for the use of SEJ to strengthen these decisions are made
Characteristics of a process for subjective probability elicitation
Get PDFThe elicitation of subjective probabilities from experts can be critical in determining a course of action when making decisions under uncertainty. A sound process to elicit probabilistic judgement is necessary to ensure that good quality data are used to inform the decision-making, as well as to provide protection to those accountable for the consequences of the determined actions. We synthesise the characteristics of a good elicitation process by critically reviewing those advocated and applied. We compare the processes inherent in the guidance produced by two professional bodies to exemplify the manner in which the characteristics manifest themselves in practice. We examine whether standardisation is meaningful given the maturity of processes for the elicitation of subjective probability
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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