Person:

Mobius, Markus

This paper builds a theory of trust based on informal contract enforcement in social networks. In our model, network connections between individuals can be used as social collateral to secure informal borrowing. We define network-based trust as the highest amount one agent can borrow from another agent, and derive a reduced-form expression for this quantity which we then use in three applications. (1) We predict that dense networks generate bonding social capital that allows transacting valuable assets, while loose networks create bridging social capital that improves access to cheap favors like information. (2) For job recommendation networks, we show that strong ties between employers and trusted recommenders reduce asymmetric information about the quality of job candidates. (3) Using data from Peru, we show empirically that network-based trust predicts informal borrowing, and we structurally estimate and test our model.

We show the existence of a pure strategy, symmetric, increasing equilibrium in dou- ble auction markets with correlated, conditionally independent private values and many participants. The equilibrium we find is arbitrarily close to fully revealing as the market size grows. Our results provide strategic foundations for price-taking behavior in large markets.

This paper shows that larger auctions are more efficient than smaller ones, but that despite this scale effect, two competing and otherwise identical markets or auction sites of different sizes can coexist in equilibrium. We find that the range of equilibrium market sizes depends on the aggregate buyer—seller ratio, and also whether the markets are especially thin.

Advances in communication and transportation technologies have the potential to bring people closer together and create a "global village." However, they also allow heterogeneous agents to segregate along special interests, which gives rise to communities fragmented by type rather than by geography. We show that lower communication costs should always decrease separation between individual agents even as group-based separation increases. Each measure of separation is pertinent for distinct types of social interaction. A group-based measure captures the diversity of group preferences that can have an impact on the provision of public goods. While an individual measure correlates with the speed of information transmission through the social network that affects, for example, learning about job opportunities and new technologies. We test the model by looking at coauthoring between academic economists before and during the rise of the Internet in the 1990s.

We decompose the beauty premium in an experimental labor market where “employers” determine wages of “workers” who perform a maze-solving task. This task requires a true skill which we show to be unaffected by physical attractiveness. We find a sizable beauty premium and can identify three transmission channels: (a) physically attractive workers are more confident and higher confidence increases wages; (b) for a given level of confidence, physically attractive workers are (wrongly) considered more able by employers; (c) controlling for worker confidence, physically attractive workers have oral skills (such as communication and social skills) that raise their wages when they interact with employers. Our methodology can be adopted to study the sources of discriminatory pay differentials in other settings.

We conduct online field experiments in large real-world social networks in order to decompose prosocial giving into three components: (1) baseline altruism toward randomly selected strangers, (2) directed altruism that favors friends over random strangers, and (3) giving motivated by the prospect of future interaction. Directed altruism increases giving to friends by 52 percent relative to random strangers, while future interaction effects increase giving by an additional 24 percent when giving is socially efficient. This finding suggests that future interaction affects giving through a repeated game mechanism where agents can be rewarded for granting efficiency enhancing favors. We also find that subjects with higher baseline altruism have friends with higher baseline altruism.