Nudge Architectures, Default Effects, and Long-Term Pension Enrolment Persistence

Occupational pension savings rates across Europe remain systematically below levels required to sustain pre-retirement living standards for the majority of workers, generating projected retirement income adequacy deficits that will intensify as demographic ageing erodes pay-as-you-go public pension systems. Behavioural economics offers a toolkit of low-cost nudge interventions — default enrolment, social norm messaging, loss and gain framing, and combined nudge architectures — that have demonstrated substantial enrolment effects in US and UK defined-contribution pension contexts, but their comparative efficacy, long-term persistence, and socioeconomic heterogeneity across Continental European pension systems has not been evaluated in a rigorous multi-country pre-registered field experiment. This study presents a pre-registered randomised field experiment conducted across 4,284 employees in six European countries — Denmark, Germany, France, the Netherlands, Poland, and Austria — testing five nudge conditions against a status quo control in the context of voluntary supplementary pension scheme enrolment. The default-on (opt-out) condition produced the largest immediate enrolment effect (62.8% vs. 18.4% in control; OR=7.42), while the combined nudge condition achieved 71.4% enrolment. Social norm messaging (44.2%) and loss framing (48.6%) produced intermediate effects. At fifty-two weeks post-intervention, enrolment persistence was highest for the default-on condition (63.2%), confirming that default effects are structurally embedded rather than dependent on continued attention. Subgroup analyses identified low-income workers and those with low financial numeracy as the highest-benefit population segments, showing enrolment effects 12–18 percentage points above the overall treatment mean, confirming the equity-improving potential of well-designed pension nudge architectures.