Motivation complementarities in prosocial behavior: Evidence from social networks of blood donors
Games and Economic Behavior · 2026 · Adrian Bruhin、Simon Haenni、Lingqing Jiang、Adrian Roethlisberger、Regula Buchli、Beat M. Frey
Abstract
If individuals’ prosocial motivations are complements, this creates an important lever for the provision of social capital. We develop a framework to identify motivation complementarities and apply it in the context of voluntary blood donations—a key example of a purely prosocial behavior. Using quasi-random phone calls to identify causal effects, we find that a 10 percentage point increase in the donation rate for a blood drive raises a focal donor’s turnout by about 5.6 percentage points, creating a policy multiplier of 2.3. We also rule out lower costs from joint traveling as the main driver of the motivation complementarities. Rather, they result, at least partly, from more general mechanisms, such as utility from social approval, peer pressure, or social image concerns.