10/27/2008 05:12 am ET | Updated May 25, 2011

Why (Your Candidate's Name Here) Will Win the Debate

This Friday, John McCain and Barack Obama will presumably (John McCain willing) square off in the first presidential debate of the season. For people like you, interested enough in politics to be reading this post, the outcome of the debate is already largely determined -- your favorite candidate will not only win the debate, but your support of the candidate will be even stronger than before, and your view of his opponent -- well, frankly, you will wonder why anyone could consider voting for him.

Debates are polarizing not simply because of their ridiculous formats, with red lights blinking when the time is up, and with embarrassing questions from the moderators followed by non-answers from the candidates. Instead, they are polarizing in large part because of the way people evaluate information on topics that they feel strongly about.

In a classic 1979 study, three Stanford psychologists recruited students who held strong opinions about the death penalty, and exposed them to hypothetical research results that either confirmed or challenged their established opinions.

Suppose you are one of the students and you begin the study already strongly opposed to the death penalty, because you don't think it deters criminals. Imagine that the researchers now present you with a brief description of a new study that demonstrates a deterrence effect. How will you respond?

As it turns out, you'll begin to waver... "Hmm, maybe I was making a hasty judgment," you'll wonder.

But now the researchers give you a longer description of the study. The study includes data from 10 states over a decade, analyzing homicide rates. Your brow begins to furrow: Only 10 states? And what about historical trends leading up to this time period? Why only one decade? And why didn't they study more common violent crimes, like armed robbery? With this more elaborate information, you confidently conclude that the study is so seriously flawed that it does nothing to challenge your preconceived notion of the death penalty.

Meanwhile, another student reads the same study. This student, unlike you, has come in to the exercise favorably inclined toward the death penalty, and is very impressed with the study design: 10 whole states! For 10 whole years!

Kind of reminiscent of the Annie Hall scene, where Diane Keaton's character is asked by her psychologist how often she and Woody's character have sex, and she replies that they have sex practically all the time, too often in fact, something like three times a week. Meanwhile, Woody's character is asked the same question by his psychologist, and provides a starkly different opinion -- reporting that they almost never have sex, barely more than three times a week.

Like the characters in Annie Hall, the students and the Stanford came to very different conclusions even though they were exposed to the same facts. Indeed, those who favored the death penalty were quite critical of studies that denied a deterrence effect, while opponents of the death penalty thought the studies were quite excellent.

The findings from the Stanford study are even more distressing than I've described so far. You see, all the students were given examples of conflicting studies -- one that proved deterrence and one that seemingly refuted it. All saw critiques of each study, as well as responses to the critiques. And the order of the studies was randomized by the researchers -- pro or con -- across students. Even the study designs were flipped around randomly: sometimes the pro-study took place in 10 states, and sometimes the con-study did.

The result? The more information students saw, the more polarized their opinions became. Pro-death penalty students became even more in favor of the death penalty, and those who were previously opposed to the death penalty became even more opposed to it.

We humans can't help but perceive evidence through the lens of our existing beliefs. McCain will really prove to his detractors what a terrible president he will be, as will Obama to his detractors.

So when you wonder how your mother-in-law can watch the same debate you watched, and completely overlook the obvious flaws in her preferred candidate, remember that she is probably wondering the same thing about you.

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