Why Incentives Don't Crowd Out Prosocial Motivation When Behavior is Driven by Mixed Motives

In this study, we suggest that crowding-out effects are unlikely when incentivizing behaviors that we refer to as mixed-motive-that is, behaviors motivated by both self-interest and prosociality. Vaccination is the prominent example we analyze: people vaccinate both to protect their own health and to contribute to herd immunity by protecting others. Building on signaling theory, we assume that people derive utility from signaling their prosociality. Incentives can crowd out prosocial motivation when they block the opportunity to send a clear prosocial signal, as in purely prosocial behaviors like charitable giving. Mixed-motive behaviors differ: they never allow for a clean prosocial signal in the first place, because self-interest is always a plausible motive. As such, providing financial incentives does not further constrain signaling opportunities, and we therefore predicted no crowding-out effects to emerge when incentivizing mixed-motive behaviors. Experimental evidence supports this prediction, and the pattern aligns with field studies suggesting that incentives may not crowd out vaccination uptake.