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Corporate focus, residential assets, and the performance of French REITs
No full textInternational audienceThis paper raises the question of the specific impact of the share of residential assets on the performance of real estate investment trusts (REITs). In the literature, many articles questioning the importance of the nature of assets held in general (and residential assets in particular) do not take the level of diversification of REITs into account. We incorporate this factor into our analysis and integrate our measure of the effects of residential assets in a framework controlling for the impact of the diversification of the type of real estate assets held. Based on French data, we question whether REITs holding residential assets perform better than REITs holding little or no residential assets for a given level of diversification. We do not detect any significant diversification effect on the performances of French REITs. We also test the impact of asset diversification on REITs market volatility. We provide some evidence that firms with strongly concentrated balance sheets are more volatile than diversified firms, but this effect is weaker for REITs holding mostly residential rather than other types of assets
Assigning Topics to Documents by Successive Projections
No full textTopic models provide a useful tool to organize and understand the structure of large corpora of text documents, in particular, to discover hidden thematic structure. Clustering documents from big unstructured corpora into topics is an important task in various areas, such as image analysis, e-commerce, social networks, population genetics. A common approach to topic modeling is to associate each topic with a probability distribution on the dictionary of words and to consider each document as a mixture of topics. Since the number of topics is typically substantially smaller than the size of the corpus and of the dictionary, the methods of topic modeling can lead to a dramatic dimension reduction. In this paper, we study the problem of estimating topics distribution for each document in the given corpus, that is, we focus on the clustering aspect of the problem. We introduce an algorithm that we call Successive Projection Overlapping Clustering (SPOC) inspired by the Successive Projection Algorithm for separable matrix factorization. This algorithm is simple to implement and computationally fast. We establish theoretical guarantees on the performance of the SPOC algorithm, in particular, near matching minimax upper and lower bounds on its estimation risk. We also propose a new method that estimates the number of topics. We complement our theoretical results with a numerical study on synthetic and semi-synthetic data to analyze the performance of this new algorithm in practice. One of the conclusions is that the error of the algorithm grows at most logarithmically with the size of the dictionary, in contrast to what one observes for Latent Dirichlet Allocation
An Exact Method for Assortment Optimization under the Nested Logit Model
No full textWe study the problem of finding an optimal assortment of products maximizing the expected revenue, in which customer preferences are modeled using a Nested Logit choice model. This problem is known to be polynomially solvable in a specific case and NP-hard otherwise, with only approximation algorithms existing in the literature. We provide an exact general method that embeds a tailored Branch-and-Bound algorithm into a fractional programming framework. Contrary to the existing literature, in which assumptions are imposed on either the structure of nests or the combination and characteristics of products, no assumptions on the input data are imposed. Although our approach is not polynomial in the input size, it can solve the most general problem setting for large-size instances. We show that the fractional programming scheme’s parameterized subproblem, a highly non-linear binary optimization problem, is decomposable by nests, which is the primary advantage of the approach. To solve the subproblem for each nest, we propose a two-stage approach. In the first stage, we fix a large set of variables based on the single-nest subproblem’s newly-derived structural properties. This can significantly reduce the problem size. In the second stage, we design a tailored Branch-and-Bound algorithm with problem-specific upper bounds. Numerical results show that the approach is able to solve assortment instances with five nests and with up to 5,000 products per nest. The most challenging instances for our approach are those with a mix of nests’ dissimilarity parameters, where some of them are smaller than one and others are greater than one. Keywords: combinatorial optimization, revenue management, assortment optimization, fractional programming, nested logit
Des connaissances aux compétences : la formation aux métiers de la transition
No full textInternational audienc
Digital upskill in a telework environment: overview of the literature and the DIGITUP project’s results
No full textA Model of Hospital Congestion with Imperfect Referral System
No full textNational audienceThis paper explains the observed hospital congestion by physicians' decision to unconditionally refer patients to hospitals, and explain why such a choice is rational when congestion deteriorates the efficiency of the tirage process at the hospital level. In an imperfect information environment, physicians might refer to top-tier hospitals patients with mild diseases that could be properly addressed by regular hospitals, just to fulfill patients' demand for the best care. Yet, the tirage capability of top-tier hospitals declines if the hospital is subject to congestion, which, in turn, provides incentives to physicians to refer more patients to these hospitals. The model presents two equilibria, one with perfect triage, and another with triage errors and hospital congestion. In this last equilibrium, a higher hospital size raises the likelihood of congestion. Public policies strategies to overcome this issue are discussed. © 2021 Editions Dalloz Sirey. All rights reserved
Freight-on-Transit for urban last-mile deliveries: A Strategic Planning Approach
No full textWe study a delivery strategy for last-mile deliveries in urban areas which combines freight transportation with mass mobility systems with the goal of creating synergies contrasting negative externalities caused by transportation. The idea is to use the residual capacity on public transport means for moving freights within the city. In particular, the system is such that parcels are first transported from origins (central distribution centers) to drop-in stations, which are stop locations on public vehicles itineraries. Then, they are transported through public vehicles to drop-out stations, from where they are delivered to destination by freighters using green vehicles (such as bikes, drones, porters, etc.). The system is known as Freight-On-Transit (FOT). In this paper, we focus on the strategic decisions related to defining the public transportation network that will take part to the delivery system, i.e., which public vehicle lines and stop locations will be included (and thus equipped for the service). We propose different formulations for the problem and effective heuristic solution approaches based on column generation. We perform exhaustive tests aimed at providing managerial insights on the performance and the efficiency of the system
Does Holding Elections during a Covid-19 Pandemic Put the Lives of Politicians at Risk?
No full textWe estimate the impact of French town hall elections held in mid-March 2020 on themortality of 163,000 male candidates aged above 60. Their excess mortality during Marchand April was similar to the general population. We compare candidates in cities withtwo candidate lists to those in cities with only one list, as elections are more intense incontacts in the former group. We also use a regression discontinuity design and investigatemortality in 2020 depending on how candidates fared in the 2014 election. We cannot detectany causal effect of active participation in the 2020 elections on mortality
L’hyperréalisme induit par les images en ultra-haute définition : Quand l'amélioration de la qualité de l'image détériore l'expérience de visionnage
No full textInternational audienceCe document examine l’impact de l'amélioration de la qualité technique des images télévisées sur l’expérience de visionnage. Nous avons mené 17 entretiens semi-directifs et 2 réunions de groupes (impliquant 20 personnes) afin de mieux comprendre l'effet des images de la télévision à haute définition sur la perception de l'expérience de visionnage des répondants, dans un environnement écologique. Trois résultats principaux ressortent des données collectées : (1) Les répondants perçoivent clairement la différence de qualité entre les images UHD et HD ; (2) La qualité de l'image procure un sentiment de fidélité à la réalité et d'immersion ; (3) Cette fidélité à la réalité n'est pas toujours attractive pour les répondants ; le sentiment d'hyperréalisme (celui d’aller au-delà de ce que l'œil pourrait observer dans une scène réelle) peut être dérangeant, surtout dans les cas de contenu non fictionnel. Ce travail suggère que tous les programmes ne devraient pas utiliser la qualité UHD et/ou que les utilisateurs devraient garder le contrôle de la définition des images qu'ils veulent voir
Managing skunkworks to achieve ambidexterity: The Robinson Crusoe effect
No full textInternational audienceLiterature on ambidexterity emphasizes the need for both exploration and exploitation. Large firms usually choose to implement structural ambidexterity to separate both activities. We here focus on an extreme case of such structural partitioning implemented as a secret skunkworks project in a large French automotive company. A qualitative survey using both primary and secondary data shows that the major basic and initial characteristics of a skunkworks (i.e. secrecy, urgency, and autonomy) created favorable conditions for the technological exploration. However, exploitation failed due to precisely those same characteristics coupled with the fact that the project did not respond to a specific market demand: The skunkworks suffered from what we call the "Robinson Crusoe effect." We therefore contribute to the literature on skunkworks, which have remained understudied in the academic literature, as well as on ambidexterity, by showing how the interrelation between different factors is crucial for structural ambidexterity to be successful