Cobra Effect · Thinking and evidence
The availability heuristic
Vivid stories make rare dangers feel common.
6 cards, read aloud in 2:29, with a test and sources.
Which is more common: an English word starting with K, or one with K in third place?
Most people say the first. Words that start with K come to mind at once. Kitchen, king, kettle. Words with K third are harder to summon. Ask, bike, like. There are about twice as many of them.
Amos Tversky and Daniel Kahneman put that question in 1973.
They were studying how people judge how often things happen. Their finding was simple. We do not count. We try to remember examples. If examples come easily, we assume the thing is common.
That is the availability heuristic.
A heuristic is a shortcut. This one swaps a hard question, how frequent is this, for an easy one, how quickly can I think of a case. Usually that works, because common things are easy to recall. It breaks when something is easy to recall for another reason. Because it was vivid. Because it was recent. Because it was on the news.
Which is why people fear the plane and not the car.
A crash that kills 200 people is on every front page for a week. Roughly the same number die on American roads every two days, and it makes no front page at all. Per mile, flying is far safer. But the plane crash is available, and the car crashes are not.
After September 2001, the fear had a body count of its own.
Many Americans stopped flying and drove instead. The psychologist Gerd Gigerenzer worked out what that cost. In the year after the attacks, roughly 1,600 extra people died on the roads. They were avoiding the danger they could picture, by taking the one they couldn’t.
The fix is to notice the feeling, and then go and count.
When a risk feels big, ask why it feels big. Is it common, or is it just easy to picture? Then look for the number. Deaths per year. Cases per thousand. Anything counted rather than remembered. The story in your head is a sample of what was memorable, not of what happens.
Sources
- Availability: A heuristic for judging frequency and probability, Amos Tversky and Daniel Kahneman, 1973. The original paper, in Cognitive Psychology. The letter K experiment is in it. Search the title with the year for a copy.
- Thinking, Fast and Slow, Daniel Kahneman, 2011. Chapters 12 and 13 are availability, including the causes of death study and why the news makes rare risks feel common.
- Dread risk, September 11, and fatal traffic accidents, Gerd Gigerenzer, 2004. The first estimate, for the three months after the attacks, in Psychological Science. His 2006 follow up in Risk Analysis put the full year at about 1,600. Short and sobering.
Nearby ideas
- Base rate neglect. A good test for a rare thing still gives mostly false alarms.
- The narrative fallacy. We invent causes for events because stories feel like explanations.
- Survivorship bias. The failures you never see can reverse the lesson you draw.
- Hindsight bias. Once you know the ending, it always looks obvious.
- Outcome bias. Judge a decision by what was known, not by how the dice fell.
- The framing effect. The same facts, worded differently, lead to different choices.
- Loss aversion. Losing something hurts about twice as much as gaining it pleases.
- The curse of knowledge. Once you know something, you cannot see what a beginner is missing.