Behavioural Spillovers Unpacked

Previous studies have shown that our past pro-social actions influence our future ones. So, which pro-social deeds inspire us to do more? Can nudges promoting these deeds crowd out this behavioural spillover? We study a social norm nudge promoting vegetarianism in an online experiment (n=2775). Our findings suggest that those who chose vegetarian options were more likely to donate to environmental charities. However, the social norm nudge crowds out donations among a population segment that initially responded positively to the nudge. Despite their appeal, social norm nudges may, therefore, be counterproductive. Our empirical strategy stems from a model describing how acting pro-socially affects individuals' willingness to do extra pro-social actions and how nudges can crowd out or crowd in this willingness. We identify these effects with an instrumental variable and explore heterogeneity with machine learning