We test the hypothesis that "genuine" or "convincing" smiling is a costly signal that has evolved to induce cooperation in situations requiring mutual trust. Potential trustees in a trust game made video clips for viewing by potential trusters before the latter decided whether to send them...

Two recent failures of the United States intelligence system have led to the creation of high-level investigative commissions. The failure to prevent the terrorist attacks of 9/11 prompted the creation of the 9/11 Commission, and the mistaken belief that Saddam Hussein had retained weapons of...

We develop two different social network models with different economic foundations. In the local-aggregate model, it is the sum of friends' efforts in some activity that affects the utility of each individual while, in the local-average model, it is costly to deviate from the average effort of...

We survey the literature on social networks by putting together the economics, sociological and physics/applied mathematics approaches, showing their similarities and differences. We expose, in particular, the two main ways of modeling network formation. While the physics/applied mathematics...

We consider a dynamic model of network formation where agents form and sever links based on the centrality of their potential partners. We show that the existence of capacity constrains in the amount of links an agent can maintain introduces a transition from dissortative to assortative...

This paper studies whether conformism behavior affects individual outcomes in crime. We present a social network model of peer effects with ex-ante heterogeneous agents and show how conformism and deterrence affect criminal activities. We then bring the model to the data by using a very detailed...

We analyze a model of network formation with agents that belong to different communities and an endogenous cost structure. Both individual benefits and costs depend on direct as well as indirect connections. Benefits of an indirect connection decrease with distance in the network, while the cost...

We analyze delinquent networks of adolescents in the United States. We develop a theoretical model showing who the key player is, i.e. the criminal who once removed generates the highest possible reduction in aggregate crime level. We also show that key players are not necessary the most active...

In order to understand the different characteristics observed in real-world networks, one needs to analyze how and why networks form, the impact of network structure on agents' outcomes, and the evolution of networks over time. For this purpose, we combine a network game introduced by Ballester...

We analyze the intergenerational transmission of the strength of religion focusing on the interplay between family and peer effects. We develop a theoretical model suggesting that both peer quality and parental effort are of importance for the religious behavior of the children. We then bring...