People behave pro-socially in a wide variety of situations that standard economic theory is unable to explain. Social comparison is one explanation for such pro-social behavior: people contributeif others contribute or cooperate as well....

Empirical evidence is provided for the importance of non-reciprocal pro-social behavior of individuals in an anonymous, n-person pure public good setting. A unique panel data set of 136,000 observations is matched with an extensive survey....