One of psychology’s big discoveries is our almost irresistible tendency to judge the likelihood of events by how mentally available they are—a mental shortcut that Daniel Kahneman and Amos Tversky identified as “the availability heuristic.” Thus anything that makes information pop into mind—its vividness, recency, or distinctiveness—can make it seem commonplace. (Kahneman explores the power of this concept at length in Thinking Fast and Slow, which stands with William James’ Principles of Psychology on my short list of greatest-ever psychology books.)
My favorite example of the availability heuristic at work is people’s misplaced fear of flying. As I document in the upcoming Psychology, 11th Edition, from 2009 to 2011 Americans were—mile for mile—170 times more likely to die in a vehicle accident than on a scheduled flight. When flying, the most dangerous part of our journey is typically the drive to the airport. In a late 2001 essay, I calculated that if—because of 9/11—we in the ensuing year flew 20 percent less and instead drove half those unflown miles, about 800 more people would die. German psychologist Gerd Gigerenzer later checked my estimate against actual traffic fatalities (why didn’t I think to do that?) and found that traffic fatalities did, indeed, jump after 9/11. Thanks to those readily available, horrific mental images, terrorists had killed more people on American highways than died on those four ill-fated planes.
The availability heuristic operates in more mundane ways as well. This morning I awoke early at an airport hotel, where I had been waylaid after a flight delay. The nice woman working the breakfast bar told me of how she, day after day, meets waylaid passengers experiencing weather problems, crew delays, and mechanical problems. Her conclusion (from her mentally available sample of flyers): something so often goes awry that if she needed to travel, she would never fly.
Vivid examples make us gasp. Probabilities we hardly grasp.