Rewarding Altruism? A Natural Field Experiment

We present evidence from a natural field experiment involving nearly 100,000 individuals on the effects of offering economic incentives for blood donations. Subjects who were offered economic rewards to donate blood were more likely to donate, and more so the higher the value of the rewards. They were also more likely to attract others to donate, spatially alter the location of their donations towards the drives offering rewards, and modify their temporal donation schedule leading to a short-term reduction in donations immediately after the reward offer was removed. Although offering economic incentives, combining all of these effects, positively and significantly increased donations, ignoring individuals who took additional actions beyond donating to get others to donate would have led to an under-estimate of the total effect, whereas ignoring the spatial effect would have led to an over-estimate of the total effect. We also find that individuals who received a reward by surprise were less likely to donate after the intervention than subjects who received no reward, suggesting that for some individuals a surprise reward adversely affected their intrinsic motivations. We discuss the implications of these findings for understanding pro-social behavior.