Geography and social links shape economic interactions. In industries, schools, and markets, the entire network determines outcomes. This paper analyzes a large class of games and obtains a striking result. Equilibria depend on a single network measure: the lowest eigenvalue. This paper is the...

I discuss the measurement of world poverty and inequality, with particular attention to the role of purchasing power parity (PPP) price indexes from the International Comparison Project. Global inequality increased with the latest revision of the ICP, and this reduced the global poverty line...

One lingering puzzle is why voluntary contributions to public goods decline over time in experimental and real-world settings. We show that the decline of cooperation is driven by individual preferences for imperfect conditional cooperation. Many people's desire to contribute less than others,...

Due to betrayal aversion, people take risks less willingly when the agent of uncertainty is another person rather than nature. Individuals in six countries (Brazil, China, Oman, Switzerland, Turkey, and the United States) confronted a binary-choice trust game or a risky decision offering the...

I study the transmission of collective memory as a mechanism for cultural transmission, in the presence of social externalities associated with individual cultural investment decisions. The younger generation's decisions depend on beliefs about the quality of existing institutions, norms, and...

We study the emergence of norms of cooperation in experimental economies populated by strangers interacting indefinitely. Can these economies achieve full efficiency even without formal enforcement institutions? Which institutions for monitoring and enforcement facilitate cooperation? Finally,...

Charness et al. (2007b) have shown that group membership has a strong effect on individual decisions in strategic games when group membership is salient through payoff commonality. In this comment, I show that their findings also apply to nonstrategic decisions, even when no outgroup exists, and...

New ideas, products, and practices take time to diffuse, a fact that is often attributed to some form of heterogeneity among potential adopters. This paper examines three broad classes of diffusion models -- contagion, social influence, and social learning -- and shows how to incorporate...