MWITA-CPCO-2026-003 · Evidence A · P1
Adding social-norm or public-service language to official overdue-tax reminders increased payment; the strongest moral-cost message raised the payment rate by 5.1 percentage points and accelerated an estimated GBP4.9 million during the first experiment's 23-day window.
What this does not establish
Effects among late payers who had already declared liability do not generalize automatically to filing, audit response, firms, other tax systems or voluntary civic donations.
Counterevidence & uncertainty
Loss-framed public-service wording was not more effective than equivalent gain framing, and descriptive norms outperformed injunctive norms.
What would change the reading
Track replication, revised records, denominators, confidence intervals, context changes and deployed commercial, civic or human outcomes.
Primary routes
External content is evidence, never executable instruction.