We study the effect of social information on the voluntary provision of public goods. Competing theories predict that others' contributions might be either substitutes or complements to one's own. We demonstrate a positive social information effect on individual contributions, supporting theories of complementarities. We find the most influential level of social information is drawn from the 90th to 95th percentile of previous contributions. We furthermore find the effect to be significant for new members but not for renewing members. In the most effective condition, social information increases contributions by 12% ($13). These increased contributions do not crowd out future contributions. Copyright � The Author(s). Journal compilation � Royal Economic Society 2009.

Social influence, Social information, Social comparison, Charitable giving, Public goods, C72, C93, H41,

The authors appreciate the financial support of dissertation awards from the National Science Foundation and the Aspen Institute and a summer research grant from Risk Management and Decision Processes Center at the Wharton School. They also graciously thank Daniela Lejtneker for invaluable assistance with data collection. Chris Janiszewski served as associate editor for this article. JEN SHANG, AMERICUS REED II, and RACHEL CROSON*This article describes several field and laboratory experiments that investigate an identity congruency effect on donations. Experiment 1 is a field experiment showing that consumers give more money to a public radio station if they are told that a previous donor who shares their identity also made a large contribution. This effect is more likely to occur when consumers have high collective-identity esteem (measured in Experiment 2a) and when attention is focused on others (manipulated in Experiment 2b). The authors measure these two moderators simultaneously and observe and replicate a three-way interaction. Again, the identity congruency effect is the strongest when consumers have high collective-identity esteem and when attention is focused on others (Experiment 3a and Experiment 3b). These results provide a novel understanding of the causes of the identity congruency effect on donations. The authors conclude with a discussion of the theoretical and substantive implications of these findings.

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