Negative Spillover Effects of Opt-out Defaults: Evidence from Organ Donation Policies

Many of today’s pressing societal challenges,such as the shortage of organs for transplantation, low vaccination rates, or the progression of climate change,requiresignificant changes in individual behavior. One promising intervention to encourage such behavioral change is the opt-out default, which presumes consent to a desirable behavior rather than relying on people to actively opt in. However, past research mainly studied how opt-out defaults affect the targeted behavior but largely omitted the possibility of negative spillover effects on related behaviors. Here, we study the possibility of such negative spillover effectson living organ donation (the related behavior) when countries switch to opt-out organ donation targeted at deceased donation. Analyzingepidemiological panel data from countries that switched to an opt-out default between 2000 and 2019,we show that switching to an opt-out default policy, on average, increased deceasedorgan donors by 2.79 per million population (pmp)––i.e., a relative uplift of +18% in the targeted behavior––but also decreased livingorgan donors by -3.56 pmp––i.e., a relative drop of -62% in a related behavior––resulting in an overall net-zero effect. Using a comparativecountry survey and experiment, we demonstrate that this reduced willingness for living altruistic (vs. familial) donations is attributable to people being less willing to become a living donor because they hold stronger beliefs that the organ supply is sufficientlymet under opt-out (vs. opt-in). Our research advances insights into the unintended consequences of default nudgesand offers initial suggestions on how to overcome negative spillover effects.