Customers write book reviews for Amazon.com and rate stores at BizRate.com. Car drivers call up radio stations to report traffic jams or radar traps. In many cases individuals share their information to the benefit of an unknown group of recipients, even though doing so is costly for the...

We introduce the give-or-destroy game that allows us to fully elicit an individual s social preference schedule. We find that about one third of the population exhibits both pro-social and anti-social preferences that are independent of payoff comparisons with those who are affected. We call...