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Jay Hamilton and Scott de Marchi have a lot in common. They are both professors at Duke University, they are roughly the same age, and they have the same number of children. And yet their consumption preferences are polar opposites. So the two professors developed a model to explain why seemingly similar people make vastly different decisions. Their book, You Are What You Choose, explores how certain attributes — such as a willingness to take risks, or worrying about what others think — affect our choices. De Marchi and Hamilton talked to TIME about their model, what it can predict and why anyone would ever want to drive a Prius.

How did you come up with the idea for the book?
Hamilton: Well, Scott and I are friends. We look very similar to marketers. But if you go a little deeper, you find that we approach life very differently. Scott's never voted. I vote in every election, and I have my kids come with me to hand out literature at the polls. He doesn't like team sports, whereas I'm a baseball coach. We wanted to explore people's decision-making styles. We came up with a model that can predict things that normal demographics can't — whether you got the flu shot, how you feel about gay marriage, your political involvement. We used 30,000 individuals who filled out surveys to predict how people make decisions.

You named the model you created TRAITS. What does that acronym stand for?
Hamilton: TRAITS stands for Time, Risk, Altruism, Information, me-Too and Stickiness. Time is whether you're focused on right now or the future. Risk is whether you're willing to take a risk. Altruism is whether you think about others. Information is whether you research before you make a decision. Me-Too is whether you look to others for guidance. Stickiness, whether you stick with what you've already done.

One of the examples you provide is that you can determine what alcoholic drinks people prefer on the basis of their TRAITS.
Hamilton: Having already taken into account age, income and gender, we can ask you a bunch of questions like how frequently you exercise, how frequently you go to the dentist each year, whether you consider the resale value of your car when you make a purchase — things that deal with the future. [Placing a high value on the future is] associated with driving a hybrid car and drinking red wine. Folks high on the me-Too factor drink whatever people around them drink. People with a high level of brand loyalty — which we find out by determining how many types of cuisine you like, how many cars you looked at before you made a decision — drink domestic beers.

What can you tell about someone who drives a Prius?
De Marchi: Prius drivers get a big kick out of their car's altruism, but they also smile because they've joined an ideological team. In a way, it is fundamentally irrational to buy a Prius. If you want to save the environment, you can buy a Honda Civic or another car that's almost as fuel efficient and way cheaper. With the money you save you can buy a chunk of the rain forest or carbon credits. You don't buy a Prius because you want to do all you can to save the environment; you also want other people to see you in the Prius. You've joined an exclusive club.

What can TRAITS explain that normal demographics don't?
De Marchi: Let me use the flu shot for an example. You'd think that people who had gotten the flu a lot or had a bad flu experience would get the vaccine every year. They didn't. Experience alone had no effect on whether you get the flu shot. But if you factored in whether someone was risk averse (they didn't want the flu again) or altruistic (they cared about infecting other people), then you could predict who would get a flu shot.

Hamilton: [Take] same-sex marriage. We think of it as a political-party issue, but being a Democrat or Republican doesn't really determine your opinion. It's really your taste for risk in life.

Risk takers approve of gay marriage?
Hamilton: If you're willing to tolerate risk in your life, you're willing to take a risky position. If you're the type of person who cares about others, you're also more likely to support same-sex marriage. If you like to gather a lot of information when you're making choices, that tips you toward approving of same-sex relationships. If you're high on the me-Too factor and you know people who are gay or lesbian, that makes you more willing to support same-sex partners. That works in our statistical model, and I think that works in Dick Cheney's life too.

What can't TRAITS explain?
Hamilton: We could predict whether you'd go for healthy food or fast food, but we can't predict chocolate or vanilla. We can tell if you'd support a third-party, independent or major-party candidate, but we don't do a good job predicting who is a Democrat vs. a Republican.

De Marchi: We got about 75%-80% of people right, but there's still more work that could be done. For the me-Too trait, we'd love to know who you know. If you look at other people to make decisions, we need to know what their preferences are before we can determine yours.

• Claire Suddath
• In a new book, 'You Are What You Choose,' Duke University professors Jay Hamilton and Scott de Marchi explain how personality traits influence decision-making