On the Number of Bidders and Auction Performance: when More Means Less

We first show in the context of sequential multi-unit auctions under complete information that a seller’s revenue may increase or decrease as the number of buyers increases, even when the additional bidders win an object. We use data from the Quebec daily hog auction to empirically analyze the effect of invitations extended to bidders from Ontario. Our estimation accounts for the endogenous timing of these rare invitations, but we nevertheless uncover a negative “invitation” effect. We attribute this anti-competitive effect to the fact that the addition of bidders increases competition in late rounds, but not necessarily in early ones

Preprocessing for classification of sparse data: application to trajectory recognition

International audienceOn one hand, sparse coding, which is widely used in signal processing, consists of representing signals as linear combinations of few elementary patterns selected from a dedicated dictionary. The output is a sparse vector containing few coding coefficients and is called sparse code. On the other hand, Multilayer Perceptron (MLP) is a neural network classification method that learns non linear borders between classes using labeled data examples. The MLP input data are vectors, usually normalized and preprocessed to minimize the inter-class correlation. This article acts as a link between sparse coding and MLP by converting sparse code into convenient vectors for MLP input. This original association assures in this way the classification of any sparse signals. Experimental results obtained by the whole process on trajectories data and comparisons to other methods show that this approach is efficient for signals classification

L’Échelle du climat de prévention de la violence : traduction, adaptation et évaluation psychométrique de la version canadienne-française

Introduction: Violence in psychiatric settings has negative consequences on patients, staff, and the institution alike. Efforts to prevent violence cannot currently be assessed due to a lack of suitable indicators. The Violence Prevention Climate Scale (VPC-14) is a validated tool that can be filled out by both staff and patients to assess the violence prevention climate in mental health care units. Objective: This study aimed to conduct the translation and adaptation of the VPC-14 to a French Canadian context, and to assess its psychometric properties in general and forensic psychiatric settings. Methods: This study followed a transcultural approach for validating measuring instruments. Psychometric properties were assessed in 308 patients and staff from 4 mental health and forensic hospitals in Quebec (Canada). Content validity was assessed using a bilingual participant approach. Internal validity was examined through exploratory factor analysis and internal consistency for each care setting using Cronbach’s alpha coefficient analysis. Results: The Échelle modifiée du climat de prévention de la violence [Modified Violence Prevention Climate Scale] (VPC-M-FR) consists of 23 items with a 3-factor structure: 1) staff action, 2) patient action, and 3) the therapeutic environment. Cronbach’s alphas ranging from 0.69 to 0.89 were obtained for the internal consistency of the scale. Discussion and conclusion: The VPC-M-FR has satisfactory psychometric properties for measuring the violence prevention climate in mental health and forensic settings. By measuring the violence prevention climate from the standpoint of patients and staff, targeted preventive measures can be implemented to improve safety for all.Introduction : La violence en milieu psychiatrique entraîne des conséquences néfastes pour les patients, les intervenants et les organisations. Pourtant, les efforts pour la prévenir ne peuvent être évalués faute d’indicateurs adéquats. Le Violence Prevention Climate Scale (VPC-14), complété par les intervenants et les patients, est un outil validé qui évalue le climat de prévention de violence. Objectif : Cette étude vise à traduire et adapter le VPC-14 au contexte québécois et à en vérifier la fiabilité et la validité en psychiatrie générale et légale. Méthodes : En se basant sur la méthode de validation transculturelle d’instruments de mesure, les propriétés psychométriques ont été évaluées auprès de 308 patients et intervenants de 4 hôpitaux et instituts de santé mentale et médico-légale québécois. La validité de construit a été examinée par une analyse factorielle exploratoire et la cohérence interne par l’analyse du coefficient alpha de Cronbach. Résultats : L’Échelle modifiée du climat de prévention de la violence (VPC-M-FR) comprend 23 énoncés avec une structure à 3 facteurs : 1) les actions des intervenants, 2) les actions des patients et 3) l’environnement thérapeutique. Des coefficients alpha de Cronbach variant de 0,69 à 0,89 ont été obtenus pour la consistance interne de l’échelle. Discussion et conclusion : Le VPC-M-FR possède des propriétés psychométriques satisfaisantes pour mesurer le climat de prévention de la violence en milieu de santé mentale et médico-légal. En tenant compte de la perspective des intervenants et des patients, des interventions ciblées de prévention pourront être mises en œuvre afin d’améliorer la sécurité de tous

Predicting effects of monotony on driver’s vigilance

Monotony has been identified as a contributing factor to road crashes. Drivers’ ability to react to unpredictable events deteriorates when exposed to highly predictable and uneventful driving tasks, such as driving on Australian rural roads, many of which are monotonous by nature. Highway design in particular attempts to reduce the driver’s task to a merely lane-keeping one. Such a task provides little stimulation and is monotonous, thus affecting the driver’s attention which is no longer directed towards the road. Inattention contributes to crashes, especially for professional drivers. Monotony has been studied mainly from the endogenous perspective (for instance through sleep deprivation) without taking into account the influence of the task itself (repetitiveness) or the surrounding environment. The aim and novelty of this thesis is to develop a methodology (mathematical framework) able to predict driver lapses of vigilance under monotonous environments in real time, using endogenous and exogenous data collected from the driver, the vehicle and the environment. Existing approaches have tended to neglect the specificity of task monotony, leaving the question of the existence of a “monotonous state” unanswered. Furthermore the issue of detecting vigilance decrement before it occurs (predictions) has not been investigated in the literature, let alone in real time. A multidisciplinary approach is necessary to explain how vigilance evolves in monotonous conditions. Such an approach needs to draw on psychology, physiology, road safety, computer science and mathematics. The systemic approach proposed in this study is unique with its predictive dimension and allows us to define, in real time, the impacts of monotony on the driver’s ability to drive. Such methodology is based on mathematical models integrating data available in vehicles to the vigilance state of the driver during a monotonous driving task in various environments. The model integrates different data measuring driver’s endogenous and exogenous factors (related to the driver, the vehicle and the surrounding environment). Electroencephalography (EEG) is used to measure driver vigilance since it has been shown to be the most reliable and real time methodology to assess vigilance level. There are a variety of mathematical models suitable to provide a framework for predictions however, to find the most accurate model, a collection of mathematical models were trained in this thesis and the most reliable was found. The methodology developed in this research is first applied to a theoretically sound measure of sustained attention called Sustained Attention Response to Task (SART) as adapted by Michael (2010), Michael and Meuter (2006, 2007). This experiment induced impairments due to monotony during a vigilance task. Analyses performed in this thesis confirm and extend findings from Michael (2010) that monotony leads to an important vigilance impairment independent of fatigue. This thesis is also the first to show that monotony changes the dynamics of vigilance evolution and tends to create a “monotonous state” characterised by reduced vigilance. Personality traits such as being a low sensation seeker can mitigate this vigilance decrement. It is also evident that lapses in vigilance can be predicted accurately with Bayesian modelling and Neural Networks. This framework was then applied to the driving task by designing a simulated monotonous driving task. The design of such task requires multidisciplinary knowledge and involved psychologist Rebecca Michael. Monotony was varied through both the road design and the road environment variables. This experiment demonstrated that road monotony can lead to driving impairment. Particularly monotonous road scenery was shown to have the most impact compared to monotonous road design. Next, this study identified a variety of surrogate measures that are correlated with vigilance levels obtained from the EEG. Such vigilance states can be predicted with these surrogate measures. This means that vigilance decrement can be detected in a car without the use of an EEG device. Amongst the different mathematical models tested in this thesis, only Neural Networks predicted the vigilance levels accurately. The results of both these experiments provide valuable information about the methodology to predict vigilance decrement. Such an issue is quite complex and requires modelling that can adapt to highly inter-individual differences. Only Neural Networks proved accurate in both studies, suggesting that these models are the most likely to be accurate when used on real roads or for further research on vigilance modelling. This research provides a better understanding of the driving task under monotonous conditions. Results demonstrate that mathematical modelling can be used to determine the driver’s vigilance state when driving using surrogate measures identified during this study. This research has opened up avenues for future research and could result in the development of an in-vehicle device predicting driver vigilance decrement. Such a device could contribute to a reduction in crashes and therefore improve road safety

Exporters’ Preferences over Import Protection Instruments when Markets are Volatile

We develop a theoretical framework showing that import demand shocks and export supply shocks can increase, keep constant, or reduce the expected level of trade relative to the volume of trade in the absence of volatility. The effect of volatility can be magnified or mitigated by the type of trade policy instrument used by an importing country. In the absence of volatility, the gains from trade for an exporting country can be reproduced whether an importing country uses a specific tariff, an ad valorem tariff or a tariff‐rate quota (TRQ). This equivalence is generally not robust to the introduction of volatility and exporting countries’ preferences vis‐à‐vis the type of trade barriers they face is influenced by the convexity of the import demand and export supply functions and the nature of the shocks. We show that the expected level of trade need not increase for the exporting country’s expected trade gains to rise. This result also holds when perfect competition is relaxed in favor of Cournot competition. Empirical evidence from the estimation of a commodity gravity model about trade in corn confirms the pertinence of accounting for the volatility of daily futures prices. The positive effect exerted by daily variations in futures prices on annual bilateral trade flows is augmented by an interaction effect for the use of non‐ad valorem tariffs

On the Number of Bidders and Auction Performance: when More Means Less

We first show in the context of sequential multi-unit auctions under complete information that a seller’s revenue may increase or decrease as the number of buyers increases, even when the additional bidders win an object. We use data from the Quebec daily hog auction to empirically analyze the effect of invitations extended to bidders from Ontario. Our estimation accounts for the endogenous timing of these rare invitations, but we nevertheless uncover a negative “invitation” effect. We attribute this anti-competitive effect to the fact that the addition of bidders increases competition in late rounds, but not necessarily in early ones

Non-Equivalent Ad Valorem Equivalents and Gravity

Specific tariffs are more commonly applied in agriculture than in the rest of the economy. We argue that the volatility of agricultural commodity markets is a contributing factor by showing that higher expected welfare can be achieved with the optimal specific tariff than with its ad valorem counterpart in the presence of volatile market conditions in the exporting countries. Contrary to popular wisdom, more volatility does not warrant higher tariffs unless the distribution of the foreign autarky price is negatively skewed. For arbitrary specific tariffs, the transformation into ad valorem equivalents may decrease or increase the volume of trade and the world price. We also show that countries with more restrictive specific tariffs are less likely to pursue tariff simplification. We estimate a gravity model about beef trade and find that specific tariffs have a small reducing effect, beyond the effect stemming from their ad valorem equivalent rate

ON THE NUMBER OF BIDDERS AND AUCTION PERFORMANCE: WHEN MORE MEANS LESS

Dans un contexte d’enchères séquentielles multi-unitaires, en information complète, on montre que le revenu du vendeur peut augmenter ou diminuer lorsque le nombre d’enchérisseurs augmente, et ce même si un des nouveaux enchérisseurs gagne un des objets. Nous avons recours à des données de l’enchère électronique du porc pour analyser empiriquement l’incidence d’enchérisseurs additionnel sur le prix moyen. Notre méthode d’estimation tient compte de l’endogénéité des invitations lancées à des abattoirs à l’extérieur du Québec. Nous avons identifié un effet négatif que nous expliquons par le fait que l’ajout d’enchérisseurs augmente la concurrence sur les derniers lots mis en vente, mais pas nécessairement sur les premiers......We first show in the context of sequential multi-unit auctions under complete information that a seller’s revenue may increase or decrease as the number of buyers increases, even when the additional bidders win an object. We use data from the Quebec daily hog auction to empirically analyze the effect of invitations extended to bidders from Ontario. Our estimation accounts for the endogenous timing of these rare invitations, but we nevertheless uncover a negative “invitation” effect. We attribute this anti-competitive effect to the fact that the addition of bidders increases competition in late rounds, but not necessarily in early ones