Abstract
Many important activities, such as charitable giving, voting, and paying taxes, are difficult to explain by the narrow self-interest hypothesis. In a large number of laboratory experiments, the self-interest hypothesis was rejected with respect to contributions to public goods (e.g., John O. Ledyard, 1995). Recent theories on pro-social behavior focus on "conditional cooperation": people are assumed to be more willing to contribute when others contribute. This behavior may be due to various motivational reasons, such as conformity, social norms, or reciprocity. According to the theory of conditional cooperation, higher contribution rates are observed when information is provided that many others contribute. This prediction is not trivial: if people behave according to pure altruism theories (e.g., Charles Clotfelter, 1997), they reduce their own contribution when informed that others are already contributing.
Testing for social comparison in the field encounters many difficulties (e.g., Charles Manski, 2000). For example, a positive correlation between expectations about the mean behavior of the reference group and one's own behavior is consistent with conditional cooperation, but not conclusive, as causality is not clear. Behavior may influence expectations, and not the other way round. Only a few laboratory experiments circumvent these problems and explicitly test conditional cooperation (e.g., Urs Fischbacher et al., 2001). These studies conclude that roughly 50 percent of people increase their contribution if others do so as well. To our knowledge, this paper is the first to go further and to test conditional cooperation in a field experiment.
Our field experiment about charitable giving supports the theory of conditional cooperation: contributions increase, on average, if people know that many others contribute. The effect varies, however, depending on past contribution behavior. Those who never contributed do not change their behavior, while people who are indifferent about contributions react most strongly to information about others' behavior. Section I presents the field experiment and the empirical strategy to test the hypotheses, Section II shows the results, and Section III offers concluding remarks.