Nicholas Evangelopoulos  Anna Sidorova  Stergios Fotopoulos  Indushobha Chengalur-Smith 《统计学通讯:模拟与计算》2013,42(8):1647-1662

This article addresses the problem of estimating the time of apparent death in a binary stochastic process. We show that, when only censored data are available, a fitted logistic regression model may estimate the time of death incorrectly. We improve this estimation by utilizing discrete-event simulation to produce simulated complete time series data. The proposed methodology may be applied to situations where time of death cannot be formally determined and has to be estimated based on prolonged inactivity. As an illustration, we use observed monthly activity patterns from 300 real Open Source Software development projects sampled from Sourceforge.net.  相似文献   

    

Alexander Bauer  Claudia Czado  Thomas Klein 《Revue canadienne de statistique》2012,40(1):86-109

We propose a new type of multivariate statistical model that permits non‐Gaussian distributions as well as the inclusion of conditional independence assumptions specified by a directed acyclic graph. These models feature a specific factorisation of the likelihood that is based on pair‐copula constructions and hence involves only univariate distributions and bivariate copulas, of which some may be conditional. We demonstrate maximum‐likelihood estimation of the parameters of such models and compare them to various competing models from the literature. A simulation study investigates the effects of model misspecification and highlights the need for non‐Gaussian conditional independence models. The proposed methods are finally applied to modeling financial return data. The Canadian Journal of Statistics 40: 86–109; 2012 © 2012 Statistical Society of Canada  相似文献   

    

Nicholas J. Higham 《Wiley Interdisciplinary Reviews: Computational Statistics》2009,1(2):251-254

This article aimed at a general audience of computational scientists, surveys the Cholesky factorization for symmetric positive definite matrices, covering algorithms for computing it, the numerical stability of the algorithms, and updating and downdating of the factorization. Cholesky factorization with pivoting for semidefinite matrices is also treated. Copyright © 2009 John Wiley & Sons, Inc. This article is categorized under:

• Algorithms and Computational Methods > Numerical Methods

  相似文献   

    

Michelle K. Ryan  S. Alexander Haslam 《英国管理杂志》2009,20(1):13-16

Adams, Gupta and Leeth ( British Journal of Management , 2008) question the universality of the glass cliff after finding no differences in US companies' financial performance either before or after the appointment of male and female CEOs. We agree that glass cliffs are neither universal nor ineluctable, but urge caution in interpreting this null result. This is because the nature and significance of women's precarious leadership positions becomes more apparent when one goes beyond archival financial data and compares the broad circumstances of male and female leaders. Here multiple strands of research suggest that above the glass ceiling the playing field for men and women is far from level.  相似文献   

    

Gilles Chemla  Michel A. Habib  Alexander Ljungqvist 《Journal of the European Economic Association》2007,5(1):93-121

Shareholder agreements govern the relations among shareholders in privately held firms, such as joint ventures and venture capital‐backed companies. We provide an economic explanation for key clauses in such agreements—namely, put and call options, tag‐along and drag‐along rights, demand and piggy‐back rights, and catch‐up clauses. In a dynamic moral hazard setting, we show that these clauses can ensure that the contract parties make efficient ex ante investments in the firm. They do so by constraining renegotiation. In the absence of the clauses, ex ante investment would be distorted by unconstrained renegotiation aimed at (i) precluding value‐destroying ex post transfers, (ii) inducing value‐increasing ex post investments, or (iii) precluding hold‐out on value‐increasing sales to a trade buyer or the IPO market. (JEL: G34)  相似文献   

    

Alberto Alesina  Alexander F. Wagner 《Journal of the European Economic Association》2006,4(4):770-799

We use data on announced and actual exchange rate arrangements to ask which countries follow de facto regimes different from their de iure ones, that is, do not do what they say. Our results suggest that countries with poor institutional quality have difficulty in maintaining pegging and abandon it often. In contrast, many countries with relatively good institutions display fear of floating, that is, they manage more than announced, perhaps to signal their differences from those countries incapable of maintaining promises of monetary stability. (JEL: F3, O1)  相似文献   

    

Kimberly M. Thompson  Radboud J. Duintjer Tebbens  Mark A. Pallansch  Olen M. Kew  Roland W. Sutter  R. Bruce Aylward  Margaret Watkins  Howard Gary  James P. Alexander  Linda Venczel  Denise Johnson  Victor M. Cáceres  Nalinee Sangrujee  Hamid Jafari  Stephen L. Cochi 《Risk analysis》2006,26(6):1571-1580

The success of the Global Polio Eradication Initiative promises to bring large benefits, including sustained improvements in quality of life (i.e., cases of paralytic disease and deaths avoided) and costs saved from cessation of vaccination. Obtaining and maintaining these benefits requires that policymakers manage the transition from the current massive use of oral poliovirus vaccine (OPV) to a world without OPV and free of the risks of potential future reintroductions of live polioviruses. This article describes the analytical journey that began in 2001 with a retrospective case study on polio risk management and led to development of dynamic integrated risk, economic, and decision analysis tools to inform global policies for managing the risks of polio. This analytical journey has provided several key insights and lessons learned that will be useful to future analysts involved in similar complex decision-making processes.  相似文献   

    

Maria Leung  James H. Lambert  Alexander Mosenthal 《Risk analysis》2004,24(4):963-984

This article presents an approach to the problem of terrorism risk assessment and management by adapting the framework of the risk filtering, ranking, and management method. The assessment is conducted at two levels: (1) the system level, and (2) the asset-specific level. The system-level risk assessment attempts to identify and prioritize critical infrastructures from an inventory of system assets. The definition of critical infrastructures offered by Presidential Decision Directive 63 was used to determine the set of attributes to identify critical assets--categorized according to national, regional, and local impact. An example application is demonstrated using information from the Federal Highway Administration National Bridge Inventory for the State of Virginia. Conversely, the asset-specific risk assessment performs an in-depth analysis of the threats and vulnerabilities of a specific critical infrastructure. An illustration is presented to offer some insights in risk scenario identification and prioritization, multiobjective evaluation of management options, and extreme-event analysis for critical infrastructure protection.  相似文献   

    

Tomasz R. Bielecki  Areski Cousin  Stéphane Crépey  Alexander Herbertsson 《统计学通讯:理论与方法》2014,43(7):1362-1389

In Bielecki et al. (2014a Bielecki , T. R. , Cousin , A. , Crépey , S. , Herbertsson , A. ( 2014a ). Dynamic hedging of portfolio credit risk in a markov copula model . J. Optimiz. Theor. Applic . doi: DOI 10.1007/s10957-013-0318-4 (forthcoming) .[Crossref] , [Google Scholar]), the authors introduced a Markov copula model of portfolio credit risk where pricing and hedging can be done in a sound theoretical and practical way. Further theoretical backgrounds and practical details are developed in Bielecki et al. (2014b Bielecki , T. R. , Cousin , A. , Crépey , S. , Herbertsson , A. ( 2014b ). A bottom-up dynamic model of portfolio credit risk - Part I: Markov copula perspective . In: Recent Adv. Fin. Eng. 2012 , World Scientific (preprint version available at http://dx.doi.org/10.2139/ssrn.1844574) . [Google Scholar],c) where numerical illustrations assumed deterministic intensities and constant recoveries. In the present paper, we show how to incorporate stochastic default intensities and random recoveries in the bottom-up modeling framework of Bielecki et al. (2014a Bielecki , T. R. , Cousin , A. , Crépey , S. , Herbertsson , A. ( 2014a ). Dynamic hedging of portfolio credit risk in a markov copula model . J. Optimiz. Theor. Applic . doi: DOI 10.1007/s10957-013-0318-4 (forthcoming) .[Crossref] , [Google Scholar]) while preserving numerical tractability. These two features are of primary importance for applications like CVA computations on credit derivatives (Assefa et al., 2011 Assefa , S. , Bielecki , T. R. , Crépey , S. , Jeanblanc , M. ( 2011 ). CVA computation for counterparty risk assessment in credit portfolios . In: Bielecki , T.R. , Brigo , D. , Patras , F. , Eds., Credit Risk Frontiers . Hoboken : Wiley/Bloomberg-Press . [Google Scholar]; Bielecki et al., 2012 Bielecki , T. R. , Crépey , S. , Jeanblanc , M. , Zargari , B. ( 2012 ). Valuation and Hedging of CDS counterparty exposure in a markov copula model . Int. J. Theoret. Appl. Fin. 15 ( 1 ): 1250004 .[Crossref] , [Google Scholar]), as CVA is sensitive to the stochastic nature of credit spreads and random recoveries allow to achieve satisfactory calibration even for “badly behaved” data sets. This article is thus a complement to Bielecki et al. (2014a Bielecki , T. R. , Cousin , A. , Crépey , S. , Herbertsson , A. ( 2014a ). Dynamic hedging of portfolio credit risk in a markov copula model . J. Optimiz. Theor. Applic . doi: DOI 10.1007/s10957-013-0318-4 (forthcoming) .[Crossref] , [Google Scholar]), Bielecki et al. (2014b Bielecki , T. R. , Cousin , A. , Crépey , S. , Herbertsson , A. ( 2014b ). A bottom-up dynamic model of portfolio credit risk - Part I: Markov copula perspective . In: Recent Adv. Fin. Eng. 2012 , World Scientific (preprint version available at http://dx.doi.org/10.2139/ssrn.1844574) . [Google Scholar]) and Bielecki et al. (2014c Bielecki , T. R. , Cousin , A. , Crépey , S. , Herbertsson , A. ( 2014c ). A bottom-up dynamic model of portfolio credit risk - Part II: Common-shock interpretation, calibration and hedging issues . Recent Adv. Fin. Eng. 2012 , World Scientific (preprint version available at http://dx.doi.org/10.2139/ssrn.2245130) . [Google Scholar]).  相似文献   

    

Nicholas Scurich  Richard S. John 《Risk analysis》2014,34(4):765-770

Security of infrastructure is a major concern. Traditional security schedules are unable to provide omnipresent coverage; consequently, adversaries can exploit predictable vulnerabilities to their advantage. Randomized security schedules, which randomly deploy security measures, overcome these limitations, but public perceptions of such schedules have not been examined. In this experiment, participants were asked to make a choice between attending a venue that employed a traditional (i.e., search everyone) or a random (i.e., a probability of being searched) security schedule. The absolute probability of detecting contraband was manipulated (i.e., 1/10, 1/4, 1/2) but equivalent between the two schedule types. In general, participants were indifferent to either security schedule, regardless of the probability of detection. The randomized schedule was deemed more convenient, but the traditional schedule was considered fairer and safer. There were no differences between traditional and random schedule in terms of perceived effectiveness or deterrence. Policy implications for the implementation and utilization of randomized schedules are discussed.  相似文献