Mobile Messaging for Offline Group Formation in Prosocial Activities: A Large Field Experiment

In this paper, we use mobile messaging to leverage recipients’ social ties and encourage offline prosocial activities in groups. In particular, we conduct a randomized field experiment with 80,000 blood donors and study how behavioral interventions and economic rewards motivate offline group formation. We find that two commonly used interventions—reminder messages and individual reward—are ineffective in motivating group formation because they do not compensate donors for the cost of bringing friends. In contrast, we find that group reward—a new reward that is contingent on a donor bringing a friend—is effective in motivating group formation. Furthermore, group reward tends to attract different types of donors, especially those who are traditionally less active in online social settings but have more local social ties. Structural estimation further reveals the underlying mechanisms, suggesting that group reward is four times more cost-effective than individual reward in driving total donation. Our study suggests that motivating offline group formation is a promising approach to boost prosocial activities.