Rosenblat, Tanya; Mobius, Markus

Quarterly Journal of Economics Vol. 124 no. 4 (November 2009): 1815-1851.

We conduct online field experiments in large real-world social networks in order to decompose prosocial giving into three components: (1) baseline altruism toward randomly selected strangers, (2) directed altruism that favors friends over random strangers, and (3) giving motivated by the prospect of future interaction. Directed altruism increases giving to friends by 52 percent relative to random strangers, while future interaction effects increase giving by an additional 24 percent when giving is socially efficient. This finding suggests that future interaction affects giving through a repeated game mechanism where agents can be rewarded for granting efficiency enhancing favors. We also find that subjects with higher baseline altruism have friends with higher baseline altruism.

JEL Classification: C90

Keywords: social networks, modified dictator games, directed altruism, enforced reciprocity