Bramoullé

Publications

Diffusion and targeting centralityJournal articleYann Bramoullé et Garance Genicot, Journal of Economic Theory, Volume 222, pp. 105920, 2024

This paper studies the dynamics of information diffusion within networks, encompassing both general and targeted dissemination. We first characterize the theoretical foundations of diffusion centrality. Next, we introduce two extensions of diffusion centrality: targeting centrality and reachability, that we believe to better capture situations involving targeted requests. We derive general explicit formulas for the computation of these novel centrality measures.

Altruism networks and economic relationsJournal articleYann Bramoullé et Rachel E. Kranton, Journal of Economic Behavior & Organization, Volume 226, pp. 106687, 2024

What patterns of economic relations arise when people are altruistic rather than strategically self-interested? What are the welfare implications of altruistically-motivated choices of business partners? This paper introduces an altruism network into a simple model of choice among partners for economic activity. With concave utility, agents effectively become inequality averse towards their friends and family. Rich agents preferentially choose to work with poor friends despite productivity losses. These preferential contracts can also align with welfare since the poor benefit the most from income gains and these gains can outweigh the loss in output. Hence, network inequality—the divergence in incomes within sets of friends and family—is key to how altruism shapes economic activity, output, and welfare. When skill homophily —the tendency for friends to have the skills needed for high production—is high, preferential contracts and productivity losses disappear since rich agents have poor friends with the requisite qualifications.

Formal insurance and altruism networksJournal articleTizié Bene, Yann Bramoullé et Frédéric Deroian, Journal of Development Economics, Volume 171, pp. 103335, 2024

We study how altruism networks affect the demand for formal insurance. Agents with CARA utilities are connected through a network of altruistic relationships. Incomes are subject to a common shock and to a large individual shock, generating heterogeneous damages. Agents can buy formal insurance to cover the common shock, up to a coverage cap. We find that ex-post altruistic transfers induce interdependence in ex-ante formal insurance decisions. We characterize the Nash equilibria of the insurance game and show that agents act as if they are trying to maximize the expected utility of a representative agent with average damages. Altruism thus tends to increase demand of low-damage agents and to decrease demand of high-damage agents. Its aggregate impact depends on the interplay between demand homogenization, the zero lower bound and the coverage cap. We find that aggregate demand is higher with altruism than without altruism at low prices and lower at high prices. Nash equilibria are constrained Pareto efficient.

Violence against Rich Ethnic Minorities: A Theory of Instrumental ScapegoatingJournal articleYann Bramoullé et Pauline Morault, Economica, Volume 88, Issue 351, pp. 724-754, 2021

Historically and in many parts of the developing world, ethnic minorities have played a central role in the economy. Examples include Chinese throughout South-east Asia, Indians in East Africa, and Jews in medieval Europe. These rich minorities are often subject to popular violence and extortion, and are treated ambiguously by local politicians. We analyse the impact of the presence of a rich ethnic minority on violence and on interactions between a rent-seeking local elite and a poor majority. We find that the local elite can always make use of the rich minority to maintain its hold on power. When the threat of violence is high, the government may change its economic policies strategically to sacrifice the minority to popular resentment. We investigate the conditions under which such instrumental scapegoating emerges, and the forms it takes. We then introduce some social integration, capturing, for instance, mixed marriages and shared education. Social integration reduces violence and yields qualitative changes in economic policies. Overall, our results help to explain documented patterns of violence and segregation.

Altruism and Risk Sharing in NetworksJournal articleRenaud Bourlès, Yann Bramoullé et Eduardo Perez-Richet, Journal of the European Economic Association, Volume 19, Issue 3, pp. 1488-1521, 2021

We provide the first analysis of the risk-sharing implications of altruism networks. Agents are embedded in a fixed network and care about each other. We explore whether altruistic transfers help smooth consumption and how this depends on the shape of the network. We find that altruism networks have a first-order impact on risk. Altruistic transfers generate efficient insurance when the network of perfect altruistic ties is strongly connected. We uncover two specific empirical implications of altruism networks. First, bridges can generate good overall risk sharing, and, more generally, the quality of informal insurance depends on the average path length of the network. Second, large shocks are well-insured by connected altruism networks. By contrast, large shocks tend to be badly insured in models of informal insurance with frictions. We characterize what happens for shocks that leave the structure of giving relationships unchanged. We further explore the relationship between consumption variance and centrality, correlation in consumption streams across agents, and the impact of adding links.

Peer Effects in Networks: A SurveyJournal articleYann Bramoullé, Habiba Djebbari et Bernard Fortin, Annual Review of Economics, Volume 12, Issue 1, pp. 603-629, 2020

We survey the recent, fast-growing literature on peer effects in networks. An important recurring theme is that the causal identification of peer effects depends on the structure of the network itself. In the absence of correlated effects, the reflection problem is generally solved by network interactions even in nonlinear, heterogeneous models. By contrast, microfoundations are generally not identified. We discuss and assess the various approaches developed by economists to account for correlated effects and network endogeneity in particular. We classify these approaches in four broad categories: random peers, random shocks, structural endogeneity, and panel data. We review an emerging literature relaxing the assumption that the network is perfectly known. Throughout, we provide a critical reading of the existing literature and identify important gaps and directions for future research.

Manufacturing Doubt: How Firms Exploit Scientific Uncertainty to Shape RegulationBook chapterYann Bramoullé et Caroline Orset, In: A Research Agenda for Environmental Economics, Matthias Ruth (Eds.), 2020, pp. 215-230, Edward Elgar Publishing, 2020

Many regulations with first-order economic and environmental consequences have to be adopted under significant scientific uncertainty. Examples include tobacco regulations in the second half of the 20th century, climate change regulations and current regulations on pesticides and neonicotinoid insecticides. Firms and industries have proved adept at exploiting such scientific uncertainty to shape and delay regulation. The main strategies documented include: hiring and funding dissenting scientists, producing and publicizing favorable scientific findings, ghostwriting, funding diversion research, conducting large-scale science-denying communication campaigns, and placing experts on advisory and regulatory panels while generally concealing involvement. In many cases, special interests have thus deliberately manufactured doubt and these dishonest tactics have had large welfare consequences.
Largely and unduly neglected by economists, these doubt-manufacturing strategies should now be addressed by the field. Here, we first present a simple theoretical framework providing a useful starting point for considering these issues. The government is benevolent but populist and maximizes social welfare as perceived by citizens. The industry can produce costly reports showing that its activity is not harmful, and citizens are unaware of the industry’s miscommunication. This framework raises important new questions, such as how industry miscommunication and citizens’ beliefs are related to scientific uncertainty. It also sheds new light on old questions, such as the choice of policy instrument to regulate pollution. We subsequently outline a tentative roadmap for future research, highlighting critical issues in need of more investigation.

Manufacturing doubtJournal articleYann Bramoullé et Caroline Orset, Journal of Environmental Economics and Management, Volume 90, Issue C, pp. 119-133, 2018

In their efforts to affect regulations, firms have developed specific strategies to exploit scientific uncertainty. They have manufactured doubt by hiring and funding dissenting scientists, by producing and publicizing favorable scientific findings and by generally concealing their involvement in biased research. We propose a new model to study the interplay between scientific uncertainty, firms' miscommunication and public policies. The government is benevolent but populist, and maximizes social welfare as perceived by citizens. The industry can produce costly reports showing that its activity is not harmful. Citizens are unaware of the industry's miscommunication. We first characterize the industry's optimal miscommunication policy. The industry notably ceases miscommunicating abruptly when scientists' belief reaches a critical threshold. We identify a natural condition under which miscommunication is stronger under a tax on emissions than under command and control. We then analyze research funding. A populist government may support research to enable firms to falsely reassure citizens. Establishing an independent research agency helps limit the welfare losses induced by populist policies.

Title lengthJournal articleYann Bramoullé et Lorenzo Ductor, Journal of Economic Behavior & Organization, Volume 150, Issue C, pp. 311-324, 2018

We document strong and robust negative correlations between the length of the title of an economics article and different measures of scientific quality. Analyzing all articles published between 1970 and 2011 and referenced in EconLit, we find that articles with shorter titles tend to be published in better journals, to be more cited and to be more innovative. These correlations hold controlling for unobserved time-invariant and observed time-varying characteristics of teams of authors.

Altruism in NetworksJournal articleRenaud Bourlès, Yann Bramoullé et Eduardo Perez-Richet, Econometrica, Volume 85, Issue 2, pp. 675-689, 2017

We provide the first analysis of altruism in networks. Agents are embedded in a fixed network and care about the well‐being of their network neighbors. Depending on incomes, they may provide financial support to their poorer friends. We study the Nash equilibria of the resulting game of transfers. We show that equilibria maximize a concave potential function. We establish existence, uniqueness of equilibrium consumption, and generic uniqueness of equilibrium transfers. We characterize the geometry of the network of transfers and highlight the key role played by transfer intermediaries. We then study comparative statics. A positive income shock to an individual benefits all. For small changes in incomes, agents in a component of the network of transfers act as if they were organized in an income‐pooling community. A decrease in income inequality or expansion of the altruism network may increase consumption inequality.