Publications des chercheurs de PSE

We consider a general equilibrium model of international trade with two layers of informational asymmetries. Private information of Home producers on costs affects the design of “behind-the-border” policies reflecting the political influence of inefficient producers. Home’s supply is contracted, causing trade, and motivating the use of tariffs. Eliminating those instruments by means of a trade agreement may become impossible once Home has also private information on its redistributive concerns. Home, when subject to strong influence by inefficient producers, might be reluctant to adopt Free Trade, which may lead to limited tariff cuts and give a role for export subsidies.

This article studies the optimal intertemporal allocation of resources devoted to the prevention of deterministic infectious diseases that admit an endemic steady- state. Under general assumptions, the optimal control problem is shown to be formally similar to an optimal growth model with endogenous discounting. The optimal dynamics then depends on the interplay between the epidemiological characteristics of the disease, the labour productivity and the degree of inter- generational equity. Phase diagrams analysis reveal that multiple trajectories, which converge to endemic steady-states with or without prevention or to the elimination of the disease, are feasible. Elimination implies initially a larger prevention than in other trajectories, but after a .nite date, prevention is equal to zero. This .sooner-the-better. strategy is shown to be optimal if the pure discount rate is su¢ ciently low.

Observing that most social networks are clustered, the literature often argues that agents are more willing to form links that close triangles. We challenge this idea by proposing a simple model of new collaboration formation that shows why network clustering may arise even though agents do not “like” network closure. We address empirically this question on the longitudinal evolution of the French co-invention network, and find that two inventors are less likely to form a first research collaboration when they have common partners. Our findings further reveal the preferences of inventors towards forming non-redundant connections.

This paper presents a benchmark stochastic endogenous growth model of an agricultural economy. Producing food requires land, and increasing the share of total land devoted to farming mechanically reduces the share of land devoted to biodiversity conservation. However, safeguarding a greater number of species guarantees better ecosystem services, which in turn ensure lower volatility of agricultural productivity. The optimal conversion/conservation rule is explicitly characterized. Value of biodiversity is considered in its function of hedging against the volatility of agricultural production. Two aspects of biodiversity’s value are examined. We first consider the total value of biodiversity as the welfare gain from biodiversity conservation, that is, the percentage increase in consumption that the society is willing to accept to give up the optimal level of biodiversity in favor of no biodiversity at all. We then consider the insurance value of biodiversity, extending the usual concepts to our stochastic dynamic framework, defining the insurance value of biodiversity as the change of the risk premium due to a marginal change in the level of biodiversity. To highlight the impact of risk on the optimal decision as in the value of biodiversity, we use the Epstein-Zin-Weil specification of preferences and represent preferences by a recursive utility function. This allows us to disentangle the effects of risk aversion and aversion to fluctuations. Thus, the preference for some rather uncertain outcomes and the propensity to smooth consumption over time are represented by two distinct parameters, and the effect of each of them are studied.

Agricultural input subsidies are often considered key instruments to increase adoption of new technologies in developing countries. Using unique experimental data from Equa- teur province in DRC, we document the e_ectiveness of such interventions in increasing households adoption of modern seed varieties (MVs). High subsidy levels increase adop- tion, in particular when other access constraints were also relieved. Demand is highly price sensitive, but demand curves do not display strong discontinuity at low prices. We _nd very limited spillover e_ects on adoption by non-voucher recipients. Adoption persists to some extent in the season that follows voucher distribution.

This paper presents a first model integrating the relation between biodiversity loss and zoonotic pandemic risks in a general equilibrium dynamic economic set-up. The occurrence of pandemics is modeled as Poissonian leaps in economic variables. The planner can intervene in the economic and epidemiological dynamics in two ways: first (prevention), by deciding to conserve a greater quantity of biodiversity to decrease the probability of a pandemic occurring, and second (mitigation), by reducing the death toll through a lockdown policy, with the collateral effect of affecting negatively labor productivity. The policy is evaluated using a social welfare function embodying society’s risk aversion, aversion to fluctuations, degree of impatience and altruism towards future generations. The model is explicitly solved and the optimal policy described. The dependence of the optimal policy on natural, productivity and preference parameters is discussed. In particular the optimal lockdown is more severe in societies valuing more human life, and the optimal biodiversity conservation is larger for more “forward looking” societies, with a small discount rate and a high degree of altruism towards future generations. Moreover, societies accepting a large welfare loss to mitigate the pandemics are also societies doing a lot of prevention. After calibrating the model with COVID-19 pandemic data we compare the mitigation efforts predicted by the model with those of the recent literature and we study the optimal prevention–mitigation policy mix.

This article studies the optimal intertemporal allocation of resources devoted to the prevention of deterministic infectious diseases that admit an endemic steady-state. Under general assumptions, the optimal control problem is shown to be formally similar to an optimal growth model with endogenous discounting. The optimal dynamics then depends on the interplay between the epidemiological characteristics of the disease, the labor productivity and the degree of intergenerational equity. Phase diagrams analysis reveals that multiple trajectories, which converge to endemic steady-states with or without prevention or to the elimination of the disease, are feasible. Elimination implies initially a larger prevention than in other trajectories, but after a finite date, prevention is equal to zero. This “sooner-the-better” strategy is shown to be optimal if the pure discount rate is sufficiently low.

How can decentralized individual decisions inefficiently reduce the ability of biodiversity to mitigate ecological and environmental variability and then its "natural insurance" role? In this article we present a simple theoretical setup to address this question and to evaluate some policy options. We study a model of strategic competition among farmers for the conversion of a natural forest to agricultural land. Unconverted forest land allows to conserve biodiversity, which contributes to reducing the volatility of agricultural production. Agents' utility is given in terms of a Kreps Porteus stochastic differential utility capable of disentangling risk aversion and aversion to fluctuations. We characterize the land used by each farmer and her welfare at the Nash equilibrium, we evaluate the overexploitation of the land and the agents' welfare loss compared to the socially optimal solution and we study the drivers of the inefficiencies of the decentralized equilibrium. After characterizing the value of biodiversity in the model, we use it to obtain a decomposition which helps to study the policy implications of the model by identifying in which cases the allocation of property rights is preferable to the introduction of a tax on land conversion. Our results suggest that enforcing property rights is more relevant in case of stagnant economies while taxing land conversion may be more suited for rapidly developing economies.