# Publications

We investigate empirically, and explain theoretically, how the relative wages of skilled and unskilled workers vary with their relative supplies in open economies. Our results combine the insights of simple labour market and trade models. In countries that trade, relative wages respond inversely to variation in skill supplies, but the response decreases with the degree of openness to trade and is small in very open countries. To reconcile our results with standard estimates of the elasticity of substitution between skilled and unskilled workers, we allow also for the influence of directed technical change and income elasticity of demand for skill-intensive goods.

We show that a monopolist's profit is higher if he refrains from collecting coarse information on his customers, sticking to constant uniform pricing rather than recognizing customers' segments through their purchase history. In the Markov perfect equilibrium with coarse information collection, after each commitment period, a new introductory price is offered to attract new customers, creating a new market segment for price discrimination. Eventually, the whole market is covered. Shortening the commitment period results in lower profits. These results sharply differ from the ones obtained when the firm can uncover the exact willingness-to-pay of each previous customer.

Cet article présente une réflexion générale sur la gouvernance et les pratiques managériales dans le domaine de l’économie sociale et solidaire (ESS) et suggère que, dans une période de mutations socioéconomiques profonde, les entreprises de l’ESS ont intérêt à mettre en place une gouvernance globale et un management des équipes qui soit cohérents avec les valeurs structurantes de son univers et les aspirations de leurs collaborateurs.

This paper analyses the evolution of COVID-19 in Cameroon over the period March 6-April 2020 using SIR models. Specifically, we 1) evaluate the basic reproduction number of the virus, 2) determine the peak of the infection and the spread-out period of the disease, and 3) simulate the interventions of public health authorities. Data used in this study is obtained from the Cameroonian Public Health Ministry. The results suggest that over the identified period, the reproduction number of COVID-19 in Cameroon is about 1.5, and the peak of the infection should have occurred at the end of May 2020 with about 7.7% of the population infected. Furthermore, the implementation of efficient public health policies could help flatten the epidemic curve.

The logarithmic prices of financial assets are conventionally assumed to follow a drift–diffusion process. While the drift term is typically ignored in the infill asymptotic theory and applications, the presence of temporary nonzero drifts is an undeniable fact. The finite sample theory for integrated variance estimators and extensive simulations provided in this paper reveal that the drift component has a nonnegligible impact on the estimation accuracy of volatility, which leads to a dramatic power loss for a class of jump identification procedures. We propose an alternative construction of volatility estimators and observe significant improvement in the estimation accuracy in the presence of nonnegligible drift. The analytical formulas of the finite sample bias of the realized variance, bipower variation, and their modified versions take simple and intuitive forms. The new jump tests, which are constructed from the modified volatility estimators, show satisfactory performance. As an illustration, we apply the new volatility estimators and jump tests, along with their original versions, to 21 years of 5-minute log returns of the NASDAQ stock price index.

This paper aims to present a new explanation for environmental traps through the presence of endogenous hazard rate. We show that adaptation and mitigation policies affect the occurrence of environmental traps differently. The former could cause environmental traps, whereas the latter could help society avoid such traps by decreasing the probability of a harmful event occurring. As a result, we present a new trade-off between adaptation and mitigation policies different than the usual dynamic trade-off that is highlighted in many studies and is crucial to developing countries. Contrary to the literature, when an economy is in a trap, an economy with a high environmental quality equilibrium tends to be more conservative in terms of resource exploitation than an economy with a low environmental quality equilibrium, which implies a heterogeneous reaction against the endogenous hazard rate.

In this article, we studied geographic variation in the use of personalized genetic testing for advanced non-small cell lung cancer (NSCLC) and we evaluated the relationship between genetic testing rates and local socioeconomic and ecological variables. We used data on all advanced NSCLC patients who had a genetic test between April 2012 and April 2013 in France in the frame of the IFCT Biomarqueurs-France study (n = 15814). We computed four established measures of geographic variation of the sex-adjusted rates of genetic testing utilization at the “départment” (the French territory is divided into 94 administrative units called ‘départements’) level. We also performed a spatial regression model to determine the relationship between département-level sex-adjusted rates of genetic testing utilization and economic and ecological variables. Our results are the following: (i) Overall, 46.87% lung cancer admission patients obtained genetic testing for NSCLC; département-level utilization rates varied over 3.2-fold. Measures of geographic variation indicated a relatively high degree of geographic variation. (ii) there was a statistically significant relationship between genetic testing rates and per capita supply of general practitioners, radiotherapists and surgeons (negative correlation for the latter); lower genetic testing rates were also associated with higher local poverty rates. French policymakers should pursue effort toward deprived areas to obtain equal access to personalized medicine for advanced NSCLC patients.

Although it is widely acknowledged that non-cognitive skills matter for adult outcomes, little is known about the role played by family environment in the formation of these skills. We use a longitudinal survey of children born in the UK in 2000–2001, the Millennium Cohort Study by the Centre for Longitudinal Studies, to estimate the effect of family size on socio-emotional skills, measured by the Strengths and Difficulties Questionnaire. To account for the endogeneity of fertility decisions, we use a well-known instrumental approach that exploits parents’ preference for children’s gender diversity. We show that the birth of a third child negatively affects the socio-emotional skills of the first two children in a persistent manner. However, we show that this negative effect is entirely driven by girls. We provide evidence that this gender effect is partly driven by an unequal response of parents’ time investment in favour of boys and, to a lesser extent, by an unequal demand for household chores.

This paper investigates the link between parental separation and children's achievement in adulthood. Using a French dataset on “Education-Training-Employment”, I first estimate a random effects model and then examine the differences in age at divorce for children within the same family, to control for divorced family selection. Three outcomes are analysed: number of years of schooling, earnings-weighted education and social position. Using a random effects model, parental separation is linked to poorer educational attainment for their children, from 32% to 12% of a standard deviation lower where the number of years of education is concerned, and from 30% to 8% of a standard deviation lower where the earnings-weighted education is concerned. This effect varies with age: least affected are the 16 to 18-year-olds, and most affected are the youngest. Where social position is concerned, effects are weaker, but remain negative. Accounting for the family fixed effect yields somewhat weaker estimated effects for the youngest, but results remain similar. Parental separation is more detrimental to boys' education under both models, but conducting a F-test, we only reject the nul hypothesis for earnings-weighted education where family fixed effect is accounted for. In results from both models, teenagers who experience a parental separation are less affected if born after 1970, but differences are not statistically different from zero where the family fixed effect is accounted for. JEL Codes: I20, J12.

The purpose of this paper is twofold. First, we examine convergence properties of an inexact proximal point method with a quasi distance as a regularization term in order to find a critical point (in the sense of Toland) of a DC function (difference of two convex functions). Global convergence of the sequence and some convergence rates are obtained with additional assumptions. Second, as an application and its inspiration, we study in a dynamic setting, the very important and difficult problem of the limit of the firm and the time it takes to reach it (maturation time), when increasing returns matter in the short run. Both the formalization of the critical size of the firm in term of a recent variational rationality approach of human dynamics and the speed of convergence results are new in Behavioral Sciences.