Within the expected-utility framework, the only explanation for risk aversion is that the utility function for wealth is concave: A person has lower marginal utility for additional wealth when she is wealthy than when she is poor. This paper provides a theorem showing that expected-utility...

In addition to pursuing their material self-interest, people are motivated to help those who are kind to them, and to hurt those who are mean to them. Such social preferences influence behavior most when material stakes are small. Rabin (1993) defin es an outcome reflecting such preferences as...