Social norms promote cooperation in everyday life because many people are willing to negatively sanction norm breakers at a cost to themselves. However, a norm violation may persist if only one person is required to sanction the norm breaker and everyone expects someone else to do it. Here we employ the volunteer’s dilemma game to model this diffusion of responsibility in social norm enforcement. The symmetric dilemma is a binary choice game in which all actors have the same costs of and benefits from cooperation and only one actor’s cooperation is required to provide the collective good for the group. The asymmetric dilemma differs from the symmetric game in one (strong) actor having lower costs of cooperation.

Here we experimentally test the hypothesis that the diffusion of responsibility effect decreases as a consequence of the switch from the symmetric to the asymmetric dilemma. In total, 252 subjects participated in our computerized laboratory experiment. In our experiment, we use the stealing game with a sanctioning option to emulate a situation in which a norm violation can be negatively sanctioned. That is, in a group of subjects, one randomly chosen subject can decide to steal money from the other group members (i.e. violate a social norm), who then face a volunteer’s dilemma as only one of them is required to reclaim the stolen amount for the entire group (i.e. enforce the social norm). We vary group size and symmetry in terms of the costs a subject incurs from sanctioning the thief.

Our results show a clear diffusion of responsibility effect in the symmetric dilemma, in which all group members have the same costs of sanctioning the thief. In the asymmetric dilemma, diffusion of responsibility is largely diminished but only after subject have played the game for some time.

By and large, these results are also borne out at the group level. In particular, heterogeneous groups become more effective in enforcing social norms as they manage to tacitly coordinate on the strongest subject to sanction the norm breaker alone. Our findings support the proposition that even relatively small asymmetries in observable sanctioning costs facilitate bystanders’ tacit coordination on the “strongest” individual to negatively sanction norm breakers. In other words, our results show how asymmetry can “break” the diffusion of responsibility in social norm enforcement and help to overcome the second-order free-rider problem (PLoS One, November 2018).