This paper examines the influence of third-party observation and third-party reward on behavior in an experimental prisoner's dilemma (PD) game. Whereas the existing literature on third-party intervention as a means to sustain social norms has dealt almost exclusively with third-party...

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 non-strategic decisions, even when no outgroup exists, and...