Data mining the heart

To be single these days is to face a sea of advice about how to attract a partner. Men are attracted to youth and beauty; women are attracted to wealth and prestige. Or are they? There's no shortage of impassioned opinion about what men and women want, yet there is little real evidence to support it. Even though finding love is one of our primary preoccupations, it has always been shrouded in mystery and guesswork. Adages like "opposites attract" feel comforting, but it would be even better to know what qualities actually entice potential partners in the real world.

To really answer the question in a scientific way, we'd need to be able to observe the behavior of thousands of single people and see whom they choose to pursue and whom they pass over. We would need a peephole into the dating world.

As it turns out, for the first time in history such a thing exists: It's called online dating. Research presented last week at the annual meeting of the American Sociological Association found that 22 percent of heterosexual couples surveyed met online, and researchers believe the Web could soon eclipse friends as the primary means of finding mates. As dating interactions have moved from the privacy of bars and social gatherings to the digital world of websites and e-mails, they are generating an unprecedented trove of data about how the initial phases of romance unfold. Online profiles contain detailed personal and demographic information about website users, and their interactions are indelibly recorded in digital form.

This mountain of information is beginning to yield intriguing findings. The dating website OKCupid has begun publishing statistics about its users' behavior on its blog, and using the numbers to generate real-world advice.

For example: Men get more responses from women if they don't smile in their profile pictures, and women find most men below average in attractiveness - but write to them anyway. More recently, the site has begun inviting collaboration with academics to do more thorough studies with the data. And in the past few years, several other researchers used data from other online dating and speed dating companies to uncover insights into what makes men and women actually respond to each other.

The sheer number of interactions makes it possible for the first time to get a detailed look at how different characteristics - weight, height, race, income, age, appearance, and political leanings, to name a few - influence a person's ability to get a date. Researchers have found, for example, that a man needs to make several extra tens of thousands of dollars to compensate for being an inch shorter, and that race matters more than people admit.

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Dan Ariely, a behavioral economist at Duke University and author of "The Upside of Irrationality," used data from a different website (he promised the site's owners anonymity) to analyze which attributes determine the success of men and women in getting responses from the opposite sex. For both sexes, the attractiveness of the photo was the most important trait (users' profile pictures were rated separately to determine how good-looking they were). Beyond that, men's height was the most important feature to women. In fact, the researchers were able to put the value of height into numbers. By comparing height to salary, they found a man who is 5 feet 9 inches tall needs to make between $35,000 and $40,000 more per year to get as many responses as a man who is 5 feet 10 inches tall.

For men, they found, a woman's most important feature was body mass index. "It turns out that men like women who are slightly anorexic," Ariely says. And unlike a man's height, there's no amount of money a woman could earn to offset the effect of higher weight. Pursuing degrees doesn't help either; education beyond a bachelor's degree for women or a master's degree for men did nothing to increase desirability. Another surprise: Smoking cigarettes actually increases a woman's popularity on dating sites, which Ariely speculates may be because men associate smoking with promiscuity.

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