What happens if you do nothing
Default
Default interventions change the choice that takes effect when the person doesn't actively choose. Opt-out organ donation, automatic retirement-plan enrollment, and pre-checked privacy settings are canonical examples. The mechanism leverages the high cost of attention and the friction of overriding the status quo.
11
Experiments
7
Policy areas
1998–2021
Year span
10 / 11
Positive
When it works
When the active-choice cost is non-trivial relative to the personal stakes, and when the default reflects what most informed people would choose anyway. Effects are typically large in absolute terms — defaults can move 20–50 percentage points in opt-in rates.
Watch out for
Defaults can override genuine individual preference, so the ethics matter. The strongest case for a default is when (a) the choice has a clearly better option for most people but high friction to choose actively, and (b) opting out is easy and visible. Defaults that hide their alternatives are manipulation, not nudge.
Default across policy areas
Public Health· 3 experiments
- Positive
Australia Plain Tobacco Packaging
Australian Government Department of Health / Cancer Council Victoria evaluation · Australia (national) · 2012
Effect: Adult daily smoking prevalence declined from 15.1% in 2010 to 11.0% in 2019, faster than the pre-policy declining trend would have predicted. Independent econometric analyses estimate plain packaging accelerated decline by 0.25-0.4 percentage points per year above counterfactual. Adolescent smoking initiation also declined notably. Industry has consistently disputed the magnitude of the effect.
- Positive
Chlorine Dispensers at Water Sources
Innovations for Poverty Action / Evidence Action · Western Kenya · 2007
Effect: Chlorine uptake: 61% vs. 10% for bottle distribution; diarrhea incidence: -26% in dispenser communities
- Positive
Organ Donation Opt-Out Defaults — Cross-National Evidence
Johnson & Goldstein (Columbia) / multiple national health ministries · Multiple countries (Europe) · 2003
Effect: Johnson & Goldstein: opt-in countries averaged 15% donor registration rates; opt-out countries averaged 98% — an 83-percentage-point difference. Wales: registered donor rate rose from 48% to 79% within 18 months of opt-out implementation. Transplant rates: significant increases in actual transplantation in opt-out countries vs. comparable opt-in countries.
Voter Engagement· 2 experiments
- Mixed
Ranked Choice Voting — New York City 2021 Mayoral Primary
New York City Board of Elections / Common Cause / Rank the Vote NYC · New York City, USA · 2021
Effect: Ballot exhaustion was approximately 14% in the final mayoral round; 84% of voters ranked multiple candidates; demographic gaps in ranking behavior were smaller than predicted (Black, Latino, and Asian voters used the full ranking similarly to white voters); winning candidates secured genuine majority coalitions rather than plurality wins. Eric Adams won with 50.4% in the eighth round.
- Positive
Automatic Voter Registration — Oregon
Oregon Secretary of State · Oregon, United States · 2016
Effect: Registration: 272,000 new registrations first year, majority low-income and younger voters; turnout of AVR registrants: comparable to traditionally registered
Energy & Environment· 2 experiments
- Positive
Green Investment Default in Retirement Plans
Nest (UK National Employment Savings Trust) · United Kingdom · 2020
Effect: 95%+ of enrolled workers now in responsible investment default; opt-out rate <2%; comparable returns
- Positive
Green Electricity Opt-Out Default
German utility companies · Germany · 2016
Effect: Opt-out adoption: 68–94% vs. opt-in: 7–41% (roughly 10× difference)