Group Size Effect on Cooperation in One-Shot Social Dilemmas

Scientific Reports 5, 7937 (2015)

8 Pages Posted: 15 Apr 2014 Last revised: 28 Jan 2015

See all articles by Helene Barcelo

Helene Barcelo

Mathematical Sciences Research Institute (MSRI)

Valerio Capraro

Middlesex University

Date Written: January 27, 2015


Social dilemmas are central to human society. Depletion of natural resources, climate protection, security of energy supply, and workplace collaborations are all examples of social dilemmas. Since cooperative behaviour in a social dilemma is individually costly, Nash equilibrium predicts that humans should not cooperate. Yet experimental studies show that people do cooperate even in anonymous one-shot interactions. In spite of the large number of participants in many modern social dilemmas, little is known about the effect of group size on cooperation. Does larger group size favour or prevent cooperation? We address this problem both experimentally and theoretically. Experimentally, we find that there is no general answer: it depends on the strategic situation. Specifically, we find that larger groups are more cooperative in the Public Goods game, but less cooperative in the N-person Prisoner's dilemma. Theoretically, we show that this behaviour is not consistent with either the Fehr & Schmidt model or (a one-parameter version of) the Charness & Rabin model, but it is consistent with the cooperative equilibrium model introduced by the second author.

Keywords: cooperation, public goods game, voluntary contribution, prisoner's dilemma, solution concepts, noncooperative game theory

JEL Classification: C70, C72, C92, C93, D74, H41

Suggested Citation

Barcelo, Helene and Capraro, Valerio, Group Size Effect on Cooperation in One-Shot Social Dilemmas (January 27, 2015). Scientific Reports 5, 7937 (2015), Available at SSRN: or

Helene Barcelo

Mathematical Sciences Research Institute (MSRI) ( email )

17 Gauss Way
Berkley, CA CH 94720
United States

Valerio Capraro (Contact Author)

Middlesex University ( email )

The Burroughs
London, NW4 4BT
United Kingdom

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