How the presentation of options shapes decisions.
What the evidence says
- People tend to stick with default options, even when alternatives exist — status quo bias and inertia mean changing requires active effort[1]
- The default effect in organ donation policy: seven presumed-consent (opt-out) European states cluster between 85.9% and 99.98% effective consent, far above the opt-in countries charted beside them (the figure shows seven; the paper’s text says ”six opt-out countries”; noted 2026-09-10 following `cpi16`). Two different kinds of evidence sit in that paper and should not be merged: the country comparison is observational, read off a figure — its own record reports ranges ”because the figure will not support more” — while the experiment is 161 respondents choosing online under opt-in, opt-out and neutral framings, ”largely eliminating effort explanations”[2]
- A nudge is any aspect of choice architecture that alters behavior predictably without forbidding options or significantly changing economic incentives[1]
- “Choice architects” can influence decisions by how they structure options — this is inevitable, so the question is whether to do it well[1]
- Key principles: set beneficial defaults, expect error, give feedback, help people understand mappings (e.g., “9 teaspoons of sugar” vs. “39 grams”), structure complex choices, align incentives[1]
- Nudges help most when decisions require scarce attention, are difficult, lack prompt feedback, or cannot be easily understood[1]
- Food placement is a classic nudge: `cpi13` presents placing healthy foods at eye level and unhealthy ones out of easy reach as changing behaviour without restricting choice — the book’s framework, not a measurement, and the eye-level evidence this library actually holds measures retail purchasing rather than eating at home; see `kpp03`[1]
- “Sludge” is the inverse of nudges — institutional frictions (paperwork, confusing interfaces) that prevent people from making beneficial choices[1]