Yves Zenou

Public information campaigns often rely on credible expert messengers to influence people's beliefs. We study how messenger identity and communication technology shape persuasion in a large-scale randomized experiment on vaccination attitudes among young adults in Greece. Participants receive an identical public-health message that varies only in who delivers it-a medical scientist or a social media influencer-and in how it is delivered-through immersive virtual reality or conventional video. Exposure raises trust in vaccines and trust in the healthcare system. Scientists are rated substantially more credible than influencers yet are no more persuasive on average; the two groups' effectiveness rests on different characteristics-the scientists' on perceived reliability and knowledgeability, the influencers' on personal appeal, prior familiarity, and reputation. We find that persuasion is greater under virtual reality, consistent with stronger engagement. Changes in beliefs persist for at least six months, and initially hesitant participants report greater willingness to vaccinate. A model in which engagement, prior uncertainty, and effective credibility enter persuasion multiplicatively rationalizes these patterns.

Public-health interventions often aspire to generate spillovers beyond the households they directly reach, but identifying who is exposed to whom within communities is challenging. Researchers frequently approximate social exposure using geographic proximity, even though the individuals who transmit health advice need not be nearby. We study this issue by conducting secondary analysis of a randomized maternal and child health counseling intervention in rural Honduras with geocoded households and mapped social networks. At our main 50-meter radius, geographic proximity captures only 30.8% of health-advice ties, while only 3.7% of geographically proximate household pairs are connected by advice-giving. The choice of exposure mapping matters for what the analysis detects. Exposure mappings based solely on geographic proximity yield a precise zero effect on diarrhea knowledge. By contrast, exposure through advice ties beyond 50 meters increases diarrhea knowledge, and the effect is statistically distinguishable from exposure through nearby non-advice contacts. The evidence suggests that simple, actionable illness-management knowledge diffuses through advice relationships that geographic proximity alone fails to capture. Reported diarrhea, indicating whether the respondent or any child had diarrhea in the previous four weeks, also increases with advice exposure outside 50m, consistent with greater recognition, recall, or reporting rather than higher underlying morbidity. We find no corresponding effects for respiratory knowledge or reported respiratory illness. Our results show that using geographic proximity as a proxy for social exposure can mask important channels of information transmission and could lead researchers to miss meaningful spillover effects.

We develop a dynamic model in which individuals allocate time between work and religious activities, and parents invest in their children's human capital and religious belief. The model delivers, in a unified framework, the two empirical regularities documented by Barro and McCleary (2003) and McCleary and Barro (2019): controlling for religious activities, stronger belief raises economic growth because it raises human capital investment; controlling for belief, more time spent on religious activities lowers growth by crowding out labor supply. While the labor-supply margin is individually optimal, the human-capital margin is not: parents do not internalize that greater human-capital investment crowds out future religious transmission through the socialization channel, leading to inefficiently high human capital in equilibrium under strong socialization externality. We extend this baseline framework in three directions. First, introducing a complementarity between religious belief and human capital-capturing the Protestant-ethic channel of Weber (1930)-we show that the efficiency of equilibrium depends non-monotonically on the strength of this complementarity. Second, allowing for cultural conflict between two religious groups à la Bisin and Verdier (2000), we show that cultural intolerance depresses human capital investment and, if human capital raises labor productivity, reduces economic growth. Third, embedding the model in a system of cities, we show that larger, more productive cities endogenously attract workers who invest more in human capital and spend less time on religious activities, generating a negative cross-city relationship between city size and religiosity that is consistent with the empirical evidence in McCleary and Barro (2019).

We study how the degree of zero-sumness in a social environment shapes cooperation and network formation. When individual gains partly come at others' expense, agents face a trade-off between contributing to a public good and extracting rents from their network position. We model this as a public good game on a directed, weighted network with a parameter capturing the intensity of zero-sum conflict. Our Zero-Sum Theorem shows that greater zero-sumness increases contributions while reducing social connectedness: agents sever links to limit exposure to extraction and increase self-provision to compensate for the diminished free-riding opportunities associated with sparser networks. The unique Nash equilibrium has contributions equal to weighted sign-alternating Bonacich centralities, reflecting how network position shapes behavior through alternating spillovers while incorporating extraction incentives. With endogenous links, equilibrium total connectivity is uniform across homogeneous agents, and heterogeneity in extraction incentives generates an inverse relationship between rent-extraction benefits and network centrality.

We develop a novel theoretical framework-the Sign-Equivalent Transformation (SET)-to analyze the mathematical structure of non-linear equilibrium systems. SET formalizes the invariance of equilibrium solutions under a class of admissible transformations and thereby provides a unified methodology for studying a broad range of economic models. We illustrate its scope by applying it to settings such as production networks, trade, spatial models, non-linear peer effects, oligopoly competition, network games, and multiplex environments. We introduce two families of nonlinear network games-one capturing strategic complementarities and the other capturing strategic substitutes-within which standard models arise as special cases. Using SET, we establish existence and uniqueness and derive new equilibrium characterization results.

In contrast to standard economic models, recent empirical evidence suggests that agents often operate based on subjective and divergent views of the competitive landscape. We develop a novel framework in which such imperfections are explicitly modeled through subjective perception networks, and introduce the concept of perception-consistent equilibrium (PCE), in which agents' actions and conjectures respond to the feedback generated by perceived competition. We establish the existence of equilibrium in broad classes of aggregative games. The model typically yields multiple equilibria, including outcomes that feature patterns of localized exclusion. Remarkably, heterogeneity in beliefs induces perceived competition rents-payoff differentials that arise purely from subjective misperceptions. We further show that PCE actions correspond to ordinal centrality measures, with eigenvector centrality emerging as a behavioral benchmark in separable payoff environments. Finally, a graph-theoretic taxonomy of PCEs reveals a hierarchical structure that ranks perceived competition rents. We also give conditions under which a unique stable equilibrium exists.

Social networks play an important role in various aspects of life. While extensive research has explored factors such as gender, race, and education in network formation, one dimension that has received less attention is the gender of one's child. Children tend to form friendships with same-gender peers, potentially leading their parents to interact based on their child's gender. Focusing on households with children aged 3-5, we leverage a rich dataset from rural Bangladesh to investigate the role of children's gender in parental network formation. We estimate an equilibrium model of network formation that considers a child's gender alongside other socioeconomic factors. Counterfactual analyses reveal that children's gender significantly shapes parents' network structure. Specifically, if all children share the same gender, households would have approximately 15% more links, with a stronger effect for families having girls. Importantly, the impact of children's gender on network structure is on par with or even surpasses that of factors such as income distribution, parental occupation, education, and age. These findings carry implications for debates surrounding coed versus single-sex schools, as well as policies that foster inter-gender social interactions among children.

We study spillover effects within co-offending networks by leveraging deaths of co-offenders for causal identification. Our results demonstrate that the death of a co-offender significantly reduces the criminal activities of other network members. We observe a decaying pattern in the magnitude of these spillover effects: individuals directly linked to a deceased offender experience the most significant impact, followed by those two steps away, and then those three steps away. Moreover, we find that the death of a more central co-offender leads to a larger reduction in aggregate crime. We also provide evidence consistent with a new theoretical prediction suggesting that the loss of a co-offender shrinks the future information set of offenders, altering their perceptions of the probability of being convicted and consequently affecting their criminal behavior. Our findings highlight the importance of understanding spillover effects for policymakers seeking to develop more effective strategies for crime prevention.