Measuring indirect reciprocity: Whose back do we scratch?

This paper presents an experimental investigation of strong indirect reciprocity. We examine both generalized indirect reciprocity (if A helps B then B helps C) and social indirect reciprocity (if A helps B then C helps A) in a setting where reciprocal behavior cannot be explained by strategic motivations, using a treatment for direct reciprocity as a benchmark. We use a variant of the strategy method to control for differences in first movers' actions across treatments. We find evidence of strong reciprocity within each treatment, for both strategies and decisions. Generalized indirect reciprocity is found to be significantly stronger than social indirect reciprocity and, interestingly, than direct reciprocity. This finding is interpreted as reflecting the relevance of first movers' motivation for second movers' reciprocal behavior. (C) 2008 Elsevier B.V. All rights reserved.