By Shankar Vedantam
Washington Post Staff Writer
Monday, October 2, 2006
Antiwar liberals last week got to savor the four most satisfying words in the English language: "I told you so."
This was after a declassified National Intelligence Estimate asserted that the war in Iraq was creating more terrorists than it was eliminating. For millions of people who opposed President Bush's mission in Iraq from the start, this was proof positive that they had been right all along. Yes, they told themselves, we saw this disaster coming.
Only . . . that isn't quite true.
One of the most systematic errors in human perception is what psychologists call hindsight bias -- the feeling, after an event happens, that we knew all along it was going to happen. Across a wide spectrum of issues, from politics to the vagaries of the stock market, experiments show that once people know something, they readily believe they knew it all along.
This is not to say that no one predicted the war in Iraq would go badly, or that the insurgency would last so long. Many did. But where people might once have called such scenarios possible, or even likely, many will now be certain that they had known for sure that this was the only possible outcome.
"Liberals' assertion that they 'knew all along' that the war in Iraq would go badly are guilty of the hindsight bias," agreed Hal Arkes, a psychologist at Ohio State University, who has studied the hindsight bias and how to overcome it. "This is not to say that they didn't always think that the war was a bad idea."
He added: "It is to say that after it was apparent that the war was going badly, they assert that they would have assigned a higher probability to that outcome than they really would have assigned beforehand."
The hindsight bias plays an important role in public debate, because it gives people a false sense of certainty. When people convince themselves that they knew something would happen, what they effectively ignore is how much that outcome may have been unpredictable.
In place of accuracy, what the hindsight bias seems to offer is a form of comfort. It is easy to be confident about the past, because one cannot be proved wrong.
While the hindsight bias is obviously self-serving, it may also be how the brain makes sense of past events, Arkes said. Once something happens, we plumb the past for pieces of evidence that led to that outcome, while ignoring all the factors that could have led to different outcomes.
One experiment documented the hindsight bias after Europe introduced a common currency. Volunteers in Austria were asked to guess how the change would affect them six months ahead of time, and then to remember what they had guessed six months after the changeover. Large numbers of people revised their recollections to match what had actually happened in the interim.
Other studies have found that once jurors hear information, asking them to disregard it is often useless. Once you know something, the hindsight bias makes it very difficult to put yourself back in the shoes of the person who did not know that piece of information.
In yet another experiment, Baruch Fischhoff, a psychologist at Carnegie Mellon University and a pioneer in the field of hindsight bias, found that Americans who made estimates about their danger after the Sept. 11, 2001, attacks recalled having made much lower estimates of risk a year later, after their fears failed to materialize.
Fischhoff testified about psychological factors in judgment at a meeting of the House intelligence committee last week.
While hindsight bias in the context of the Iraq war was real, the psychologist cautioned in an interview against misuse of the idea -- the argument by many supporters of the Bush administration that it was impossible to know ahead of time how the war would turn out.
"It's wrong for people who should be held accountable to hide behind hindsight bias and say this was totally unpredictable," Fischhoff said.
Indeed, research by both Fischhoff and Arkes show that people can fight the hindsight bias only when they honestly and systematically try to explain how different outcomes are possible. Such self-doubt is the exact opposite of how modern politics works: In the age of the blogosphere, certitude is king.
At its core, in other words, the hindsight bias is a form of overconfidence. Clearly acknowledging how you might be wrong is the only weapon against the error, Fischhoff said, but that is one thing politicians hate to do.
"Many people who are offended by the president are offended by his lack of deliberateness," Fischhoff concluded. "We want leaders who look deliberately at the evidence and are candid about the gambles they are taking. . . . A lot of unease in this country is consistent with people not feeling like they are being leveled with."