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.

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.

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.

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.

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.

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.

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.

The Oxford Handbook of the Economics of NetworksBookYann Bramoullé, Andrea Galeotti et Brian Rogers (Eds.), 2016-04, 857 pages, Oxford University Press, 2016

The Oxford Handbook of the Economics of Networks represents the frontier of research into how and why networks they form, how they influence behavior, how they help govern outcomes in an interactive world, and how they shape collective decision making, opinion formation, and diffusion dynamics. From a methodological perspective, the contributors to this volume devote attention to theory, field experiments, laboratory experiments, and econometrics. Theoretical work in network formation, games played on networks, repeated games, and the interaction between linking and behavior is synthesized. A number of chapters are devoted to studying social process mediated by networks. Topics here include opinion formation, diffusion of information and disease, and learning. There are also chapters devoted to financial contagion and systemic risk, motivated in part by the recent financial crises. Another section discusses communities, with applications including social trust, favor exchange, and social collateral; the importance of communities for migration patterns; and the role that networks and communities play in the labor market. A prominent role of networks, from an economic perspective, is that they mediate trade. Several chapters cover bilateral trade in networks, strategic intermediation, and the role of networks in international trade. Contributions discuss as well the role of networks for organizations. On the one hand, one chapter discusses the role of networks for the performance of organizations, while two other chapters discuss managing networks of consumers and pricing in the presence of network-based spillovers. Finally, the authors discuss the internet as a network with attention to the issue of net neutrality. Contributors to this volume - Daron Acemoglu Sinan Aral Lori Beaman Francis Bloch Vincent Boucher Yann Bramoulle Emily Breza Antonio Cabrales Arun Chandrasekhar Thomas Chaney Syngjoo Choi Daniele Condorelli Wouter Dessein Marcin Dziubinski Nick Economides

Introduction to the HandbookBook chapterYann Bramoullé, Andrea Galeotti et Brian W. Rogers, In: Oxford Handbook on the Economics of Networks, Yann Bramoullé, Andrea Galeotti et Brian W. Rogers (Eds.), 2016-04, pp. 3-9, 2016


Introduction to the HandbookBook chapterYann Bramoullé, Andrea Galeotti et Brian W. Rogers, In: Oxford Handbook on the Economics of Networks, Yann Bramoullé, Andrea Galeotti et Brian W. Rogers (Eds.), 2016-04, pp. 3-9, 2016