Do pecuniary incentives increase blood donation or do extrinsic incentives crowd out intrinsic incentives? In Rewarding Altruism (NBER, free) an important and impressive new paper Nicola Lacetera, Mario Macis and Robert Slonim analyze a field experiment involving some 100,000 donors and find that pecuniary incentives significantly increase blood donations. The field experiment covers a wide geographic area and the donors are tracked for a significant period of time after donating so the authors can look for geographic and temporal spillovers. The authors offered potential donors gift cards of $5, $10 and $15.
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.
Some of the increase in supply came from temporal substitution but this is not without value. Incentives are not just about increasing supply but also about increasing supply at the right time, i.e. when blood is most needed so it’s useful to have a lever that can influence when donations are made.
Crowding out did receive some support in an odd context. The authors found that donors who were surprised with a gift card after they had donated were less likely to donate in the future. Thus, the donors did not reciprocate the unexpected gift and may have felt that their altruistic intention was being undermined. Once again we see the overwhelming importance of context when trying to understand incentives. To paraphrase Mises, an incentive is not an objective fact but a subjective interpretation.
The authors did not find any decline in quality ala Titmuss. Indeed, this is to be expected since modern blood donation is not a random shout-out to people on the street but instead relies predominantly on repeat donors with a long donation history.
Gift cards of $5, $10 and $15 are small incentives and the authors suggest that the benefits from the increased supply far exceed the costs. It’s notable that it takes longer to donate blood plasma and as a result the U.S. blood plasma industry (the “OPEC of blood plasma”) has always relied on paid donors.