Proportional hazards models with continuous marks

For time-to-event data with finitely many competing risks, the proportional hazards model has been a popular tool for relating the cause-specific outcomes to covariates [Prentice et al. Biometrics 34 (1978) 541--554]. This article studies an extension of this approach to allow a continuum of competing risks, in which the cause of failure is replaced by a continuous mark only observed at the failure time. We develop inference for the proportional hazards model in which the regression parameters depend nonparametrically on the mark and the baseline hazard depends nonparametrically on both time and mark. This work is motivated by the need to assess HIV vaccine efficacy, while taking into account the genetic divergence of infecting HIV viruses in trial participants from the HIV strain that is contained in the vaccine, and adjusting for covariate effects. Mark-specific vaccine efficacy is expressed in terms of one of the regression functions in the mark-specific proportional hazards model. The new approach is evaluated in simulations and applied to the first HIV vaccine efficacy trial.Comment: Published in at http://dx.doi.org/10.1214/07-AOS554 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Uncertainty and Cooperation: Analytical Results and a Simulated Agent Society

Uncertainty is an important factor that influences social evolution in natural and artificial environments. Here we distinguish between three aspects of uncertainty. Environmental uncertainty is the variance of resources in the environment, perceived uncertainty is the variance of the resource distribution as perceived by the organism and effective uncertainty is the variance of resources effectively enjoyed by individuals. We show analytically that perceived uncertainty is larger than environmental uncertainty and that effective uncertainty is smaller than perceived uncertainty, when cooperation is present. We use an agent society simulation in a two dimensional world for the generation of simulation data as one realisation of the analytical results. Together with our earlier theoretical work, results here show that cooperation can buffer the detrimental effects of uncertainty on the organism. The proposed conceptualisation of uncertainty can help in understanding its effects on social evolution and in designing artificial social environments.Agent-Based Modelling, Cooperation, Social Interaction Simulation, Uncertainty

A Communication Framework Towards Flexible Associations of Business Entities Within Evolving Environments

The Internet and its manifestations, such as electronic commerce or in general network communication between different groups of interest (i.e., agents) have become indispensable for many of us. To adequately use the ever increasing amount of data, attempts are being made to extend data processing from a merely lexical view towards more complex, but equally important, multi-level view, including meaning and/or context (e.g., DAML, Web Services). The goal of this paper is to introduce a formal framework, apt to model communications from such a multi-level perspective. Therein, we discuss fundamental ideas of communication, such as agents involved and their respective structure. We integrate the concept of an agent's adaptive behaviour in order to assure a high degree of understanding. The framework is then illustrated using practical examples where we briefly present its usefulness and how it may be further developed. L'Internet et l'utilisation qu'on en fait, par exemple le commerce électronique ou plus généralement l'établissement de réseaux de communications entre différents intervenants (c.-à-d., agents) est devenu indispensable pour plusieurs d'entre nous. Il devient de plus en plus difficile d'utiliser adéquatement la vaste quantité de données s'y trouvant. À cette fin, de nombreuses initiatives tentent de faire évoluer les systèmes d'information les faisant passer de simples outils permettant le traitement lexical des données à des engins complexes comprenant les données et leur contexte d'interprétation (p.ex., DAML, Web Services). Dans cet article, nous présentons un cadre formel qui modélise les interactions, tout en tenant compte de plusieurs niveaux d'abstraction (p.ex., lexical, syntaxique, sémantique, etc.). Nous nous attardons aux concepts fondamentaux de la communication, tels que les agents impliqués dans les interactions et leur structure. Nous considérons aussi comment ces agents évoluent pour assurer la plus grande compréhension possible des messages reçus. Des exemples concrets servent à mieux expliquer comment le cadre peut être utilisé et comment il peut être raffiné.Inter-enterprise communication framework, information system evolution, adaptive systems., Cadre descriptif des communications inter-entreprise, évolution des systèmes d'information, systèmes adaptatifs