Stratégies gagnantes aux enchères à un sou

Abstract : I empirically analyze the behavior of the players in an online auction format, a penny auction in which each bid represents a cost to the player and increases the price of the auctioned item by a small increment above the price at the time of the bid. I examine the behavior of the players using a dataset containing 86,000 auctions and 12,8 million individual bids, provided by a penny-auction website. I develop a methodology to identify the strategies that are associated with higher profit and I expand the list of potential strategies to all observable bidding characteristics. My methodology identifies all the winning strategies already mentioned in the literature on penny auctions, but also strategies for which an intuition was provided, but no formal proof. I find that bidding on packages of tokens is the strategy that is the most highly correlated with the profit of the players. I also find that bidding on items of low value and bidding quickly after the timer is reset is associated with a higher profit. On the other side, playing standard auctions, bidding on high-value or electronic items, and bidding just before the timer expires are associated with lower profit. Using the winning strategies identified by my methodology, I then estimate the impact of a player’s experience on the use of these strategies with a mixed model to account for the heterogeneity of the players. The estimation demonstrates that players, on average, learned to use better strategies as they played more and more auctions. The biggest winners appeared to have a better understanding of the winning strategies when they started playing compared to the rest of the sample. I support this conclusion using the individual parameters provided by the mixed model.Résumé : J’analyse empiriquement le comportement des joueurs dans un format d’enchères en ligne, une enchère à un sou, dans laquelle chaque mise représente un coût pour le joueur et augmente le prix de l’article vendu aux enchères par un petit montant. J’étudie le comportement des joueurs en utilisant une base de données contenant 86,000 ventes aux enchères et 12,8 millions de mises. La base de données a été fournie par un site d’enchères à un sou. Je développe une méthodologie pour identifier les stratégies qui sont associées à des profits plus élevés et j’élargis la liste des stratégies potentielles à toutes les caractéristiques de mises observables. Ma méthodologie identifie toutes les stratégies gagnantes déjà mentionnées dans la littérature sur les enchères à un sou, mais aussi des stratégies pour lesquelles une intuition a été fournie, mais aucune preuve formelle. Je trouve que miser sur les ensembles de jetons est la stratégie qui est la plus fortement corrélée avec le profit des joueurs. Je trouve aussi que les mises sur des articles de faible valeur et des mises faite rapidement après que la minuterie soit remise à zéro est associée à un profit plus élevé. À l’opposé, jouer des enchères de type standard, miser sur des articles de valeur élevé ou des articles électroniques, et miser juste avant l’expiration de la minuterie sont des stratégies associées avec un profit plus faible. J’utilise ensuite les stratégies gagnantes identifiées par ma méthodologie pour estimer l’impact de l’expérience d’un joueur sur l’utilisation de ces stratégies. Pour ce faire, j’utilise un modèle mixte afin de tenir compte de l’hétérogénéité des joueurs. L’estimation montre qu’en moyenne, plus le nombre d’enchères auquel les joueurs ont participé augmentait, plus les joueurs ont utilisé des stratégies associées avec des profits plus élevés. J’utilise ensuite les effets individuels fournis par le modèle mixte pour démontrer que les joueurs qui ont les bénéfices les plus élevés semblaient avoir une meilleure compréhension des stratégies gagnantes lorsqu’ils ont commencé à jouer comparativement au reste des joueurs

Eric Maurin, La nouvelle question scolaire. Les bénéfices de la démocratisation

Aller à l’encontre des idées reçues en matière de démocratisation scolaire, s’inscrire à contre-courant des discours pessimistes sur les conséquences négatives de la massification, dénoncer les assertions polémiques et parfois démagogiques de ceux qui ne cessent de critiquer l’école, voilà une aventure hardie qui implique objectivité et rigueur. C’est ce que tente et réussit Éric Maurin dans son dernier ouvrage. Il s’agit là du travail d’un économiste qui, par une démarche rigoureuse dans l’a..

Telematics Combined Actuarial Neural Networks for Cross-Sectional and Longitudinal Claim Count Data

We present novel cross-sectional and longitudinal claim count models for vehicle insurance built upon the Combined Actuarial Neural Network (CANN) framework proposed by Mario W\"uthrich and Michael Merz. The CANN approach combines a classical actuarial model, such as a generalized linear model, with a neural network. This blending of models results in a two-component model comprising a classical regression model and a neural network part. The CANN model leverages the strengths of both components, providing a solid foundation and interpretability from the classical model while harnessing the flexibility and capacity to capture intricate relationships and interactions offered by the neural network. In our proposed models, we use well-known log-linear claim count regression models for the classical regression part and a multilayer perceptron (MLP) for the neural network part. The MLP part is used to process telematics car driving data given as a vector characterizing the driving behavior of each insured driver. In addition to the Poisson and negative binomial distributions for cross-sectional data, we propose a procedure for training our CANN model with a multivariate negative binomial (MVNB) specification. By doing so, we introduce a longitudinal model that accounts for the dependence between contracts from the same insured. Our results reveal that the CANN models exhibit superior performance compared to log-linear models that rely on manually engineered telematics features.Comment: 30 pages, 10 tables, 6 figure

Bayesian Network Modelling the risk analysis of complex socio technical systems

International audienceThe risk analysis of a system is a multidisciplinary process in constant evolution. Indeed, if a few years ago, analyses were limited at the technical level, it is today necessary to consider the system in a global way, by including Human beings and Organisations. But this involves an increasing complexity of the studied system, because of the widening of its limits and the diversity of considered disciplines. This article proposes a method to structure the knowledge in a decisionmaking model

Impact of cone-beam computed tomography for the identification and management of an oral portal of entry in patients with infective endocarditis. A Delphi study

Infective endocarditis (IE) is a rare and life-threatening disease. Cutaneous portal of entry (POE) is predominant for IE, but an oral POE is the second most frequent source. Thus looking for and treating an oral POE in IE patients is of critical importance in order to reduce the risk of IE relapse or recurrence. The objectives of this study were: 1) To reach a consensus on decision-making following the detection of an oral POE on cone-beam computed tomography (CBCT) while they were not identified using the current recommended approach in IE patients (oral examination and orthopantomogram: OPT). 2) To determine whether this consensus differs when regarding the microbiology of IE. Twenty oral or maxillofacial surgeons participated to this Delphi study. The questionnaire was based on five radiological cases (OPT and matching CBCT) with two scenarios according to the objectives of detecting oral POE in an IE patient (curative in case of oral causative microorganism, and preventive if not) and different therapeutic approaches (surgical or conservative treatment, no treatment) for each of them. Consensus was defined as an agreement rate of ?75%. The response rate was?85%. After four rounds, consensus was achieved for all proposals. CBCT changed the decision-making of experts in four cases. In one case, the decision was influenced by the IE microbiology toward a more radical approach in case of oral causative microorganism. In IE patients, CBCT changed markedly the decision-making of experts by eradicating more oral POE than when using OPT. This could reduce the risk of IE relapse and recurrence

L’École entre évaluation et contrôle

Dans le milieu éducatif, au cours de ces dernières décennies, les contrôles eurent mauvaise presse et semblaient archaïques. Ils disparurent en partie ou se firent très discrets. C’est alors que l’évaluation, surtout qualitative, prit un essor considérable. Trente ans après, une page se tourne. L’important développement de l’évaluation, sa variété et son omniprésence contribuent aujourd’hui à ternir son lustre et à accorder progressivement aux contrôles une place nouvelle et de plus en plus i..

On the projective geometry of the supercircle: a unified construction of the super cross-ratio and Schwarzian derivative

We consider the standard contact structure on the supercircle, S^{1|1}, and the supergroups E(1|1), Aff(1|1) and SpO(2|1) of contactomorphisms, defining the Euclidean, affine and projective geometry respectively. Using the new notion of (p|q)-transitivity, we construct in synthetic fashion even and odd invariants characterizing each geometry, and obtain an even and an odd super cross-ratios. Starting from the even invariants, we derive, using a superized Cartan formula, one-cocycles of the group of contactomorphisms, K(1), with values in tensor densities F_\lambda(S^{1|1}). The even cross-ratio yields a K(1) one-cocycle with values in quadratic differentials, Q(S^{1|1}), whose projection on F_{3/2}(S^{1|1}) corresponds to the super Schwarzian derivative arising in superconformal field theory. This leads to the classification of the cohomology spaces H^1(K(1),F_\lambda(S^{1|1})). The construction is extended to the case of S^{1|N}. All previous invariants admit a prolongation for N>1, as well as the associated Euclidean and affine cocycles. The super Schwarzian derivative is obtained from the even cross-ratio, for N=2, as a projection to F_1(S^{1|2}) of a K(2) one-cocycle with values in Q(S^{1|2}). The obstruction to obtain, for N\geq 3, a projective cocycle is pointed out.Comment: LaTeX, 50 pages. Minor improvement