A new comment by Stefan Felder challenges key conclusions of a recent study on opt-out organ donation policies. Güntürkün et al. (2025) had argued that while opt-out legislation has no significant effect on deceased organ donation, it leads to a substantial decline in living organ donations.

Felder shows that this alleged “crowding-out” effect is not robust. The original findings are highly sensitive to the composition of the control group and to assumptions about the timing of policy effects. In particular, countries such as Turkey and Cyprus—characterized by extreme volatility in living donation rates—strongly influence the results, despite failing to satisfy the parallel trends assumption required for a valid Difference-in-Differences analysis.

In addition, Güntürkün et al. assume an anticipation effect that shifts the treatment period to before the formal adoption of opt-out legislation, effectively classifying COVID-19 years as post-treatment. When this assumption is removed, the negative effect on living donations disappears entirely, while the effect on deceased donation rates becomes statistically significant and positive.

The observed declines in donation activity after 2020 are more plausibly explained by pandemic-related disruptions to health systems. This interpretation is consistent with evidence from the National Health Service and recent UK-based studies, which attribute reduced transplant activity primarily to COVID-19 rather than to changes in consent legislation.

Overall, Felder concludes that there is no credible causal evidence that opt-out organ donation policies crowd out living donations. Moreover, the behavioral mechanism proposed by Güntürkün et al.—that perceived sufficiency of deceased donors reduces willingness to donate while alive—remains empirically unsubstantiated.

Crowding-out effects of opt-out defaults: Evidence from organ donation policies | PNAS Nexus | Oxford Academic