Read the full article at NPR.

Researchers asked about 350 heterosexual undergrads at Northwestern University to fill out questionnaires assessing their personalities and romantic preferences.

They were quizzed about things like self-esteem, goals, values, loneliness, what they were looking for in a partner, and how assertive or patient or creative they want the partner to be — and how much those things apply to them, says Samantha Joel, a psychologist at the University of Utah and lead author on the study, which was published last week in Psychological Science. "Lots of traits that have been theorized to be important for relationships in past literature."

Then the participants went on four-minute speed dates and rated how attracted they felt to each person.

The researchers then designed an algorithm to try to identify what personality traits or preferences led to the in-person attraction using part of the data from both the personality surveys and the speed dating. They also asked it to predict who in the group would be attracted to whom based solely on their questionnaire answers.

The machine could figure out who the most desirable people in the bunch were based on certain characteristics like physical attractiveness, Joel says. But when it came to predicting which people would be a good fit for each other, the machine failed spectacularly.

"It predicted 0 percent [of the matches.] Some of the models we ran got a negative percentage, which means you're better off just guessing," Joel says. "I was really surprised. I thought we would be able to predict at least some portion of the variance — like extroverts or liberals like each other."

The result is a little unnerving to scientists, too.

"They're saying [real attraction] is something over and beyond what we know about what makes someone attractive," says Robin Edelstein, a psychologist at the University of Michigan who studies relationships and was not involved in the work. If the results suggest that attributes psychologists would think attract certain people are effectively useless when it comes to making matches, then what is actually going on when two people are drawn to one another?

That question has left Joel and other psychologists scratching their heads. "It's a very elusive, mysterious thing. I don't think people even know themselves what it is about a specific person," Edelstein says. "I don't know if it's about specific questions or specific traits."

There are a few flaws in the study, though. "One concern is that they're testing in a relatively small undergraduate sample," Edelstein says. College students plucked from the same campus are probably more similar to one another than those out in the wider dating world, and there isn't much scientific evidence that similar people are more attracted to one another, Edelstein says. Without a bigger range of personalities, Joel's algorithm might not have come across that magic combination of traits and preferences that makes that special someone stand out to another person.