Almost two-thirds of the third parties indeed punished the violation of the distribution norm and their punishment increased the more the norm was violated. Likewise, up to roughly 60% of the third parties punished violations of the cooperation norm. Thus, our results show that the notion of strong reciprocity extends to the sanctioning behavior of ''unaffected'' third parties.

XREF: Connects to strong reciprocity literature and evolutionary explanations of punishment behavior in economic games.

Ernst Fehr, Third-Party Punishment and …, loc. 2