Network Interventions for Changing Physical Activity Behaviour in Preadolescents.

Network interventions can help achieve behavioural change by inducing peer-pressure in the network. However, inducing peer-pressure without considering the structure of the existing social network may render the intervention ineffective or weaker. In a 7-week school-based field experiment using preadolescents' physical activity (PA) as a proxy for estimating behavioural change, we test the hypothesis that boys' and girls' distinct networks are susceptible to different social incentives. We run three different social-rewards schemes, in which classmates' rewards depend on the PA of two friends either reciprocally (directly or indirectly) or collectively. Compared to a random-rewards control, social-rewards schemes had an overall significantly positive effect on PA (51.8% increase), with females being more receptive to the direct reciprocity scheme (76.4%) and males to team (collective) rewards (131.5%). Differences in the sex-specific sub-networks can explain these findings. Network interventions adapted to the network-specific characteristics may constitute a powerful tool for behavioural change.

Inducing peer pressure to promote cooperation.

Cooperation in a large society of self-interested individuals is notoriously difficult to achieve when the externality of one individual's action is spread thin and wide on the whole society. This leads to the 'tragedy of the commons' in which rational action will ultimately make everyone worse-off. Traditional policies to promote cooperation involve Pigouvian taxation or subsidies that make individuals internalize the externality they incur. We introduce a new approach to achieving global cooperation by localizing externalities to one's peers in a social network, thus leveraging the power of peer-pressure to regulate behavior. The mechanism relies on a joint model of externalities and peer-pressure. Surprisingly, this mechanism can require a lower budget to operate than the Pigouvian mechanism, even when accounting for the social cost of peer pressure. Even when the available budget is very low, the social mechanisms achieve greater improvement in the outcome.