Brains aren't wired to buy new tally of Iraqi deaths

Huge rise to 650,000 tests mind's 'anchor'

Washington Post

Oct. 24, 2006 12:00 AM

First a history lesson: More than three decades ago, two psychologists conducted an experiment that was equal parts funny and deadly serious.

They spun a roulette wheel and when it landed on the number 10 they asked some people whether the number of African countries was greater or less than 10 percent of the United Nations. Most people guessed that estimate was too low. Maybe the right answer was 25 percent, they guessed.

The psychologists spun their roulette wheel a second time and when it landed on the number 65, they asked a second group whether African countries made up 65 percent of the United Nations. That figure was too high, everyone agreed. Maybe the correct answer was 45 percent.

The difference in the estimates of the two groups was tied to the original number they were given. It made no difference that the number was meaningless: It came from a roulette wheel. Psychologists Amos Tversky and Daniel Kahneman described the error as caused by a phenomenon known as anchoring - when you don't know the answer to something, whatever starting point you have plays a powerful role in determining what you think is the right answer.

Flash forward 32 years. A Johns Hopkins study published in a respected peer-reviewed journal finds the number of Iraqis killed as a consequence of the 2003 invasion to be about 650,000. Critics immediately get up in arms; President Bush declares the result "not credible."

Although the debate over the study has been largely driven by the political implications of the number of Iraqi casualties, psychologists say the fact that many people find the new number hard to digest is a perfect example of anchoring.

Previous estimates had put the number of Iraqi casualties at 30,000 to 50,000. Once that number was anchored in people's minds, it was a foregone conclusion that most people would find it very difficult to accept a much larger number.

It is important to remember that the psychological phenomenon does not tell you what the correct number is. But it does say that even if the 650,000 number is accurate, we are likely not to believe it.

Like many other aspects of human behavior, psychologists say, anchoring is just one way the brain makes sense of the world. We assume the information we are given is at least somewhat accurate, and therefore use that as an anchor around which to evaluate new information or make informed guesses. Like other subtle biases, anchors influence people at an unconscious level.

Is there a way to avoid the anchoring bias? In some situations, there is, said psychologist Nicholas Epley at the University of Chicago.

"In what year was George Washington elected president?" he asked. "You don't know. But you know independence was declared in 1776. You know it is later than that. Is it 1778? 1780? The anchor is in the ballpark. It gets you closer than just pulling the answer out of a hat."

What's the only way to avoid the anchoring bias altogether? Know the right answer.