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...

Prosocial behavior is crucial for tackling global challenges such as climate change, poverty, and conflict, yet people often prioritize personal benefits over the common good. A classic philosophical proposition is that prosocial behavior benefits from psychological wisdom — a concept...