Proportion dominance
Also known as: Proportionality bias
A big percentage beats a big absolute number for grabbing our attention.
What it means
The tendency to respond to the proportion or relative size of a benefit rather than its absolute magnitude, so that a high percentage saved feels more compelling than a larger number of lives or dollars saved at a lower percentage. Because a proportion is easy to evaluate on a bounded 0–100% scale while an absolute count is hard to place without a reference, people latch onto the ratio that is most 'evaluable.' This makes a program that saves 90% of 100 at-risk people seem more attractive than one that saves 20% of 1,000 — even though the latter saves more than twice as many. The effect is closely tied to evaluability and to extension neglect, and it can be reversed by making absolute numbers concrete and comparable. It matters in resource allocation, charity, and risk reduction, where the most impactful option is frequently the one with the less impressive-looking percentage.
Examples
Donors and policymakers favor saving 80% of the people at a small site over saving a far greater number who represent only 20% of those at a large site.
Airport safety equipment described as saving 98% of the 150 people at risk draws more support than equipment that simply saves 150 lives — the percentage is easy to judge, the count is not.
An engineering team celebrates wiping out 95% of the crashes in a feature nobody opens, while a fix worth 5% of the crashes on the home screen would spare far more people.
First described in Slovic and colleagues; Fetherstonhaugh et al. (1997); Bartels (2006).