La plupart des informations présentées ci-dessous ont été récupérées via RePEc avec l'aimable autorisation de Christian Zimmermann
Dynamic Frailty Count Process in Insurance: A Unified Framework for Estimation, Pricing, and ForecastingJournal articleYang Lu, Journal of Risk and Insurance, Volume 85, Issue 4, pp. 1083-1102, 2018

We study count processes in insurance, in which the underlying risk factor is time varying and unobservable. The factor follows an autoregressive gamma process, and the resulting model generalizes the static Poisson-Gamma model and allows for closed form expression for the posterior Bayes (linear or nonlinear) premium. Moreover, the estimation and forecasting can be conducted within the same framework in a rather efficient way. An example of automobile insurance pricing illustrates the ability of the model to capture the duration dependent, nonlinear impact of past claims on future ones and the improvement of the Bayes pricing method compared to the linear credibility approach.

Sovereign debt in emerging market countries: not all of them are serial defaultersJournal articleGilles Dufrénot et Anne-Charlotte Paret, Applied Economics, Volume 50, Issue 59, pp. 6406-6443, 2018

Avoiding to assign emerging market countries a ‘typical’ behaviour, this article considers the heterogeneity across them and through time to predict their sovereign default episodes. Moreover, it focuses on the imbalance between defaulted debt and GDP. For the first time, we use a panel nonlinear regime-switching model whose explanatory factors have a different impact on sovereign default, depending on the regime the country belongs to. We mitigate some common views of the literature (in particular the ‘serial default’ theory) and identify countries deserving to be monitored carefully, because of a higher exposure to sovereign default risk.Abbreviation: CRAG : Credit Rating Assessment Group; EMBI: Emerging Market Bond Index; FSI: Financial Stress Index; GDP: Gross Domestic Product; GFC: Global Financial Cycle; GTD: Gonzalez, Teräsvirta, and V. Dijk; IMF: International Monetary Fund; LM: Lagrange Multiplier; PSTR: Panel Smooth Transition Regression; PTR: Panel Threshold Regression; STAR: Smooth Transition Auto Regressive model; US: United States; VIX: Volatility Index

When do social cues and scientific information affect stated preferences? Insights from an experiment on air pollutionJournal articleDominique Ami, Frédéric Aprahamian, Olivier Chanel et Stéphane Luchini, Journal of Choice Modelling, Volume 29, Issue C, pp. 33-46, 2018

Stated preference surveys are usually carried out in one session, without any follow-up interview after respondents have had the opportunity to experience the public goods or policies they were asked to value. Consequently, a stated preference survey needs to be designed so as to provide respondents with all the relevant information, and to help them process this information so they can perform the valuation exercise properly. In this paper, we study experimentally an elicitation procedure in which respondents are provided with a sequence of different types of information (social cues and objective information) that allows them to sequentially revise their willingness-to-pay (WTP) values. Our experiment was carried out in large groups using an electronic voting system which allows us to construct social cues in real time. To analyse the data, we developed an anchoring-type structural model that allows us to estimate the direct effect (at the current round) and the indirect effect (on subsequent rounds) of information. Our results shed new light on the interacted effect of social cues and objective information: social cues have little or no direct effect on WTP values but they have a strong indirect effect on how respondents process scientific information. Social cues have the most noticeable effect on respondents who initially report a WTP below the group average but only after receiving additional objective information about the valuation task. We suggest that the construction and the provision of social cues should be added to the list of tools and controls for stated preference methods.

Entrepreneurial motivation and business performance: evidence from a French Microfinance InstitutionJournal articleRenaud Bourlès et Anastasia Cozarenco, Small Business Economics, Volume 51, Issue 4, pp. 943-963, 2018

This article examines the link between entrepreneurial motivation and business performance in the French microfinance context. Using hand-collected data on business microcredits from a Microfinance Institution (MFI), we provide an indirect measure of entrepreneurial success through loan repayment performance. Controlling for the endogeneity of entrepreneurial motivation in a bivariate probit model, we find that “necessity entrepreneurs” are more likely to have difficulty repaying their microcredits than “opportunity entrepreneurs”. However, type of motivation does not appear to make a difference to business survival. We test for the robustness of our results using parametric duration models and show that necessity entrepreneurs experience difficulties in loan repayment earlier than their opportunity counterparts, corroborating our initial findings. Our results are also robust to a sharper analysis of motivation, focusing on unemployment (on the necessity side) and non-pecuniary benefits from success (on the opportunity side).

Identifying Consensus on Coastal Lagoons Ecosystem Services and Conservation Priorities for an Effective Decision Making: A Q ApproachJournal articleMariam Maki Sy, Hélène Rey-Valette, Monique Simier, Vanina Pasqualini, Charles Figuières et Rutger De Wit, Ecological Economics, Volume 154, Issue C, pp. 1-13, 2018

Coastal lagoons ecosystems, while representing benefits for the local populations, have been subjected to high anthropogenic pressures for decades. Hence, conservation measures of these ecosystems are urgently needed and should be combined with their sustainable uses. To address these issues, new research avenues for decision support systems have emphasized the role of the assessment of ecosystem services for establishing conservation priorities by avoiding monetarization approaches. These approaches, because they flatten the various values of nature by projecting them on the single monetary dimension, are often rejected by the stakeholders. We undertake a Q analysis to identify levels of consensus and divergence among stakeholders on the prioritization of ecosystem services provided by two French Mediterranean coastal lagoons areas. The results highlighted that there is a strong consensus among categories of stakeholders in the study sites about the paramount importance of regulation and maintenance services. Three groups of stakeholders, each sharing the same points of view regarding ecosystem services conservation, were identified for each study site. As a non-monetary valuation, Q methodology is very instrumental for the new pluralistic approach of decision support by capturing the values expressed by the stakeholders, without triggering a rejection reflex due to the monetarization.

Federal minimum wage hikes do reduce teenage employment. A replication study of Bazen & Marimoutou (Oxford Bulletin of Economics and Statistics, 2002)Journal articleStephen Bazen et Vêlayoudom Marimoutou, International Journal for Re-Views in Empirical Economics (IREE), Volume 2, Issue 2018-5, pp. 1-13, 2018

In 2002 we published a paper in which we used state space time series methods to analyse the teenage employment-federal minimum wage relationship in the US (Bazen and Marimoutou, 2002). The study used quarterly data for the 46 year period running from 1954 to 1999. We detected a small, negative but statistically significant effect of the federal minimum wage on teenage employment, at a time when some studies were casting doubt on the existence of such an effect. In this note we re-estimate the original model with a further 16 years of data (up to 2015). We find that the model satisfactorily tracks the path of the teenage employment-population ratio over this 60 year period, and yields a consistently negative and statistically significant effect of minimum wages on teenage employment. The conclusion reached is the same as in the original paper, and the elasticity estimates very similar: federal minimum wage hikes lead to a reduction in teenage employment with a short run elasticity of around – 0.13. The estimated long run elasticity of between – 0.37 and – 0.47 is less stable, but is nevertheless negative and statistically significant.

Targeting the key player: An incentive-based approachJournal articleMohamed Belhaj et Frédéric Deroian, Journal of Mathematical Economics, Volume 79, Issue C, pp. 57-64, 2018

We consider a network game with local complementarities. A policymaker, aiming at minimizing or maximizing aggregate effort, contracts with a single agent on the network to trade effort change against transfer. The policymaker has to find the best agent and the optimal contract to offer. Our study shows that for all utilities with linear best-responses, it only takes two statistics about the position of each agent on the network to identify the key player: the Bonacich centrality and the self-loop centrality. We also characterize key players under linear quadratic utilities for various contractual arrangements.

Testing for misspecification in the short-run component of GARCH-type modelsJournal articleThomas Chuffart, Emmanuel Flachaire et Anne Péguin-Feissolle, Studies in Nonlinear Dynamics & Econometrics, Volume 22, Issue 5, pp. 1-17, 2018

In this article, a misspecification test in conditional volatility and GARCH-type models is presented. We propose a Lagrange Multiplier type test based on a Taylor expansion to distinguish between (G)ARCH models and unknown GARCH-type models. This new test can be seen as a general misspecification test of a large set of GARCH-type univariate models. It focuses on the short-term component of the volatility. We investigate the size and the power of this test through Monte Carlo experiments and we compare it to two other standard Lagrange Multiplier tests, which are more restrictive. We show the usefulness of our test with an illustrative empirical example based on daily exchange rate returns.

TCR and CD28 Concomitant Stimulation Elicits a Distinctive Calcium Response in Naive T CellsJournal articleFan Xia, Cheng-Rui Qian, Zhou Xun, Yannick Hamon, Anne-Marie Sartre, Anthony Formisano, Sébastien Mailfert, Marie-Claire Phelipot, Cyrille Billaudeau, Sébastien Jaeger, et al., Frontiers in Immunology, Volume 9, 2018

T cell activation is initiated upon ligand engagement of the T cell receptor (TCR) and costimulatory receptors. The CD28 molecule acts as a major costimulatory receptor in promoting full activation of naive T cells. However, despite extensive studies, why naive T cell activation requires concurrent stimulation of both the TCR and costimulatory receptors remains poorly understood. Here, we explore this issue by analyzing calcium response as a key early signaling event to elicit T cell activation. Experiments using mouse naive CD4+ T cells showed that engagement of the TCR or CD28 with the respective cognate ligand was able to trigger a rise in fluctuating calcium mobilization levels, as shown by the frequency and average response magnitude of the reacting cells compared with basal levels occurred in unstimulated cells. The engagement of both TCR and CD28 enabled a further increase of these two metrics. However, such increases did not sufficiently explain the importance of the CD28 pathways to the functionally relevant calcium responses in T cell activation. Through the autocorrelation analysis of calcium time series data, we found that combined but not separate TCR and CD28 stimulation significantly prolonged the average decay time (τ) of the calcium signal amplitudes determined with the autocorrelation function, compared with its value in unstimulated cells. This increasement of decay time (τ) uniquely characterizes the fluctuating calcium response triggered by concurrent stimulation of TCR and CD28, as it could not be achieved with either stronger TCR stimuli or by coengaging both TCR and LFA-1, and likely represents an important feature of competent early signaling to provoke efficient T cell activation. Our work has thus provided new insights into the interplay between the TCR and CD28 early signaling pathways critical to trigger naive T cell activation.

Qui travaille après 65 ans ?Journal articleAlain Trannoy, Insee Références, pp. 25-38, 2018

La part des personnes âgées de 65 à 74 ans qui sont en emploi est en forte croissance depuis 10 ans, même si elle ne représente encore que 5 %de cette classe d’âge. En comparaison avec les inactifs dumême âge, les actifs occupés entre 65 et 74 ans sont plus souvent des hommes, en bonne santé, plus diplômés et résidant dans l’agglomération parisienne. Les cadres salariés, mais aussi les indépendants et les agriculteurs sont surreprésentés dans ce groupe.
Comparés aux 60-64 ans en emploi, les actifs occupés entre 65 et 74 ans sont plus souvent indépendants et plus fréquemment à temps partiel quand ils sont salariés ; qu’ils soient salariés ou indépendants, leurs revenus d’activité sont plus faibles en moyenne.
Parmi les 65-74 ans en emploi, 70 %perçoivent également une pension de retraite ; ceux qui n’en perçoivent pas en parallèle sont plus souvent immigrés, de sexe féminin, en bonne santé et résidant dans l’agglomération parisienne. L’emploi de ces non-cumulants se distingue principalement par une durée de travail plus importante : 78 % sont à temps complet (contre 32 % pour ceux qui perçoivent une pension de retraite). Quatre profils types de personnes en emploi après 65 ans se dégagent : les employées peu diplômées à temps partiel, les très diplômés et très qualifiés urbains, les commerçants et enfin les agriculteurs âgés.
Enfin, parmi les déterminants extra-financiers qui sont associés à la décision de rester en emploi au-delà de 65 ans pour ceux qui étaient encore en emploi à cet âge, le non-salariat, l’absence de limitation dans les activités habituelles, la poursuite de l’activité du conjoint ou encore la faible différence d’âge avec le conjoint se détachent comme les facteurs explicatifs les plus significatifs.