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Science 4 September 2009:
Vol. 325. no. 5945, pp. 1272 - 1275
DOI: 10.1126/science.1177418
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Reports

Positive Interactions Promote Public Cooperation

David G. Rand,1,2,* Anna Dreber,1,6,* Tore Ellingsen,6 Drew Fudenberg,3 Martin A. Nowak1,4,5,{dagger}

The public goods game is the classic laboratory paradigm for studying collective action problems. Each participant chooses how much to contribute to a common pool that returns benefits to all participants equally. The ideal outcome occurs if everybody contributes the maximum amount, but the self-interested strategy is not to contribute anything. Most previous studies have found punishment to be more effective than reward for maintaining cooperation in public goods games. The typical design of these studies, however, represses future consequences for today’s actions. In an experimental setting, we compare public goods games followed by punishment, reward, or both in the setting of truly repeated games, in which player identities persist from round to round. We show that reward is as effective as punishment for maintaining public cooperation and leads to higher total earnings. Moreover, when both options are available, reward leads to increased contributions and payoff, whereas punishment has no effect on contributions and leads to lower payoff. We conclude that reward outperforms punishment in repeated public goods games and that human cooperation in such repeated settings is best supported by positive interactions with others.

1 Program for Evolutionary Dynamics, Harvard University, Cambridge, MA 02138, USA.
2 Berkman Center for Internet and Society, Harvard University, Cambridge, MA 02138, USA.
3 Department of Economics, Harvard University, Cambridge, MA 02138, USA.
4 Department of Mathematics, Harvard University, Cambridge, MA 02138, USA.
5 Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
6 Department of Economics, Stockholm School of Economics, 11358 Stockholm, Sweden.

* These authors contributed equally to this work.

{dagger} To whom correspondence should be addressed. E-mail: martin_nowak{at}harvard.edu

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