1,720,963 research outputs found
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
Measuring exposure to dependence risk with random Bernstein copula scenarios
No full textInternational audienceThis paper considers the problem of measuring the exposure to dependence risk carried by a portfolio with an arbitrary number of two-asset derivative contracts. We develop a worst-case risk measure com- puted over a set of dependence scenarios within a divergence restricted region. The set of dependence scenarios corresponds to Bernstein copulas obtained by simulating random doubly stochastic matrices. We then devise a method to compute hedging positions when a limited number of hedging instruments are available for trading. In an empirical study, we show how the proposed method can be used to re- veal an exposure to dependence risk where usual sensitivity methods fail to reveal it. We also illustrate the ability of the proposed method to generate parsimonious hedging strategies in order to reduce the exposure to dependence risk of a given portfolio.<br/
Detection of arbitrage in a market with multi-asset derivatives and known risk-neutral marginals
No full textInternational audienceIn this paper we study the existence of arbitrage opportunities in a multi-asset market when risk-neutral marginal distributions of asset prices are known. We first propose an intuitive characterization of the absence of arbitrage opportunities in terms of copula functions. We then address the problem of detecting the presence of arbitrage by formalizing its resolution in two distinct ways that are both suitable for the use of optimization algorithms. The first method is valid in the general multivariate case and is based on Bernstein copulas that are dense in the set of all copula functions. The second one is easier to work with but is only valid in the bivariate case. It relies on results about improved Fréchet–Hoeffding bounds in presence of additional information. For both methods, details of implementation steps and empirical applications are provided.<br/
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
Three essays in finance of markets
No full textLe but de cette thèse est l'étude de certains aspects d'un marché financier comportant plusieurs actifs risqués et des options écrites sur ces actifs. Dans un premier essai, nous proposons une expression de la distribution implicite du prix d'un actif sous-jacent en fonction du smile de volatilité associé aux options écrites sur cet actif. L'expression obtenue pour la densité implicite prend la forme d'une densité log-normale plus deux termes d'ajustement. La mise en œuvre de ce résultat est ensuite illustrée à travers deux applications pratiques. Dans le deuxième essai, nous obtenons deux caractérisations de l'absence d'opportunité d'arbitrage en termes de fonctions copules. Chacune de ces caractérisations conduit à une méthode de détection des situations d'arbitrage. La première méthode proposée repose sur une propriété particulière des copules de Bernstein. La seconde méthode est valable dans le cas bivarié et tire profit de résultats sur les bornes de Fréchet-Hoeffding en présence d'information additionnelle sur la dépendance. Les résultats de l'utilisation de ces méthodes sur des données empiriques sont présentés. Enfin, dans le troisième essai, nous proposons une approche pour couvrir avec des options sur spread l'exposition au risque de dépendance d'un portefeuille d'options écrites sur deux actifs. L'approche proposée repose sur l'utilisation de deux modèles paramétriques de dépendance que nous introduisons: les copules Power Frank (PF) et Power Student's t (PST). Le fonctionnement et les résultats de l'approche proposée sont illustrés dans une étude numérique.This thesis is dedicated to the study of a market with several risky assets and options written on these assets. In a first essay, we express the implied distribution of an underlying asset price as a function of its options implied volatility smile. For the density, the obtained expression has the form of a log-normal density plus two adjustment terms. We then explain how to use these results and develop practical applications. In a first application we value a portfolio of digital options and in another application we fit a parametric distribution. In the second essay, we propose a twofold characterization of the absence of arbitrage opportunity in terms of copula functions. We then propose two detection methods. The first method relies on a particular property of Bernstein copulas. The second method, valid only in the case of a market with two risky assets, is based upon results on improved Fréchet-Hoeffding bounds in presence of additional information about the dependence. We also present results obtained with the proposed methods applied to empirical data. Finally, in the third essay, we develop an approach to hedge, with spread options, an exposure to dependence risk for a portfolio comprising two-asset options. The approach we propose is based on two parametric models of dependence that we introduce. These dependence models are copulas functions named Power Frank (PF) and Power Student's t (PST). The results obtained with the proposed approach are detailed in a numerical study
Measuring exposure to dependence risk with random Bernstein copula scenarios
No full textInternational audienceThis paper considers the problem of measuring the exposure to dependence risk carried by a portfolio with an arbitrary number of two-asset derivative contracts. We develop a worst-case risk measure com- puted over a set of dependence scenarios within a divergence restricted region. The set of dependence scenarios corresponds to Bernstein copulas obtained by simulating random doubly stochastic matrices. We then devise a method to compute hedging positions when a limited number of hedging instruments are available for trading. In an empirical study, we show how the proposed method can be used to re- veal an exposure to dependence risk where usual sensitivity methods fail to reveal it. We also illustrate the ability of the proposed method to generate parsimonious hedging strategies in order to reduce the exposure to dependence risk of a given portfolio.<br/
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
Implied Distribution as a Function of the Volatility Smile
No full textInternational audienceThe aim of this paper is to obtain the risk-neutral density of an underlying asset price as a function of its option implied volatility smile. We derive a known closed form non-parametric expression for the density and decompose it into a sum of lognormal and adjustment terms. By analyzing this decomposition we also derive two no-arbitrage conditions on the volatility smile. We then explain how to use the results. Our methodology is applied first to the pricing of a portfolio of digital options in a fully smile-consistent way. It is then applied to the fitting of a parametric distribution for log-return modelling, the Normal Inverse Gaussian.<br/
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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