Opt-out defaults do not increase donation rates but can create uncertainty about the deceased’s wishes
Psychologist Ralph Hertwig gives expert testimony on organ donation to the Health Committee of the German Bundestag
On January 29, the Health Committee of the German Bundestag met to discuss a possible amendment to the Transplantation Act that would introduce an opt-out system, where all adults are presumed organ donors unless they explicitly withdraw their consent. During the debate, Ralph Hertwig, Director of Center for Adaptive Rationality at the Max Planck Institute for Human Development, was invited to provide expert testimony.

Hertwig emphasized the importance of taking empirical evidence into account alongside constitutional and ethical considerations. He cautioned against “cherry picking” when evaluating the data. Hertwig referred to a study he co-authored with colleagues from the Max Planck Institute for Human Development, the MSB Medical School Berlin, and the Max Planck Centre for Computational Psychiatry and Ageing Research, published in November 2024. In this study, the research team analyzed longitudinal data from five countries (Argentina, Chile, Sweden, Uruguay, and Wales) that switched from an opt-in to an opt-out system. In their longitudinal analyses, they examined the impact of this switch on organ donation rates. The data was collected from international registries, including the International Registry in Organ Donation and Transplantation (IRODaT) and the Global Observatory on Donation and Transplantation (GODT). Of the 39 countries that had switched to an opt-out system by 2019, only five could be included in the analysis due to a lack of historical data or because presumed consent practices often existed informally prior to formal legislation (Dallacker et al., 2024). As Hertwig testified to the committee, “We deliberately chose countries with reliable data. However, in these countries, we found no causal link between the switch to an opt-out system and an increase in organ donation rates.”
The crucial role of relatives and communicative challenges
Asked about the role of relatives, Hertwig highlighted their considerable influence in organ donation decisions. A 2012 study comparing 54 countries—25 with an opt-out system and 29 with an opt-in system—showed that in many countries, even explicit consent to donate is not sufficient if the family objects. For example, in 15 of the 19 countries with an opt-out system that provide a method for individuals to express their wish to donate, medical professionals overrule the deceased’s documented wish if the family raises objections (Rosenblum et al., 2012). “This demonstrates that the family consent’s remains crucial,” said Hertwig.
Moreover, the opt-out system poses communicative challenges. Psychological experiments show that presumed consent sends a weaker signal of underlying preference, leading to uncertainty—especially among families, who often do not know what the deceased truly wanted. An explicit consent system, in contrast, provides a clearer framework for decision making for all parties involved.
Structural measures are key
Hertwig also referred to a 2022 representative survey by the German Federal Centre for Health Education (BZgA), which showed that the proportion of people carrying an organ donor card increased from 22% in 2012 to 40% in 2022 (Zimmering & Hammes, 2023). At the same time, the actual donation rate decreased. “This means that having a larger number of potential donors does not necessarily lead to more actual organ donations. What matters are structural measures,” he emphasized. These include improving the infrastructure and ensuring the widespread availability of transplant coordinators, as demonstrated by the case of Spain.
Scientific basis for policy decisions
For years, Hertwig has advocated for behaviorally informed approaches to enhance people’s decision making. As a proponent of “boosting,” he argues that—contrary to widespread assumptions—people are capable of making competent and informed decisions. Unlike “nudging,” which subtly steers people’s choices, boosting focuses on empowering people with knowledge and skills so they can make informed decisions independently.
In a recently published review article (Herzog & Hertwig, 2025), he highlights the untapped potential of behavioral research for policymaking. His work provides valuable insights into how scientific findings can help empower individuals and promote socially sustainable decisions.
Further information
Hearing in full length on January 29 in the media library on bundestag.de
Press release “Organ donation: Opt-out defaults do not increase donation rates”; November 13, 2024
Press release “Boosting decision-making skills”; January 21, 2025