Small Quasi-Cash Rewards: A Field Experiment on Voluntary Plasma Donations

We conducted a large-scale and long lasting randomized field experiment at the donation centers of the Belgian Red Cross-Flanders to study the impact of a small extra reward for plasma donations. Donors normally receive one thank-you-coupon (worth €1.5) for a blood donation and two coupons for a plasma donation. Informing donors about these existing rewards increased plasma donations with on average 4.6% per month over a nine-month information period. Rewarding plasma donations with an extra thank-you-coupon increased plasma donations with an additional 7.1% per month over a six-month reward period. However, the extra reward for plasma decreased blood donations at donation centers with on average 3.3% per month over the reward period. Results of an additional representative survey show that a desire (i) to reciprocate the extra coupon and (ii) to respond to the extra coupon as a signal of higher needs are plausible prosocial motivations to explain the strong effect of a small extra quasi-cash reward. The survey results also suggest that our findings are not only relevant for plasma donations, but also for volunteering more generally.