Punishment to promote prosocial behavior: a field experiment

Prosocial behavior is typically promoted through behavioral interventions or modest rewards. We provide field evidence for the effectiveness of a less commonly used way to achieve the same goal: making it illegal not to engage in the desired behavior and then enforcing that rule. We partnered with a city to conduct a natural field experiment aimed at increasing the rate at which 70,000 households separate their waste. Households were informed that it was illegal not to separate their waste and that they could be fined. The announcement was followed by a month of intensive and highly conspicuous inspections of the contents of garbage containers set out for emptying. The treatment had a large and immediate positive effect on waste separation. Unlike the effects of crackdowns in typical applications such as traffic enforcement, the behavioral effect persisted at a stable rate for many months. This divergent result is consistent with a change in habits, a previously unexplored way in which law enforcement crackdowns can have a lasting effect. If habits sustain the new behavior, then this also alleviates concerns about loss of intrinsic motivation.