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Wednesday, Aug. 1, 2007 | For Fran Torley, it was a horrendous experience. Unexpectedly, she had fallen ill, and doctors were powerless to do anything about it.

“I came down with obesity two years after I got married,” the 41-year-old Oklahoma City resident told a national newspaper. “I know it was hard for my husband to watch me suffer from this disease. When he caught obesity a year later, he got so depressed, he couldn’t do anything but sit on the couch. Some days, we sit and watch television from dawn till dusk, hoping for news of a breakthrough.”

That newspaper, of course, was The Onion, a satirical publication that in 2004 wrote about scientists’ unsuccessful efforts to find a cure for obesity. Looking back, the article seemed to eerily foreshadow last week’s news, when researchers announced that they had found evidence that obesity is “socially contagious.”

Even the venerable New York Times caught the obesity bug, reporting Wednesday that obesity “can spread from person to person, much like a virus.”

The new report, co-authored by University of California, San Diego, political science professor James Fowler, was indeed groundbreaking — just not in the way many media reports have suggested.

While Fowler and his colleague did find evidence that you gain weight when your friends do, their conclusions do little to suggest that obesity is an infectious disease. If it were a pathogen spread through human contact, we would expect that you would grow larger when your neighbor does, and that your nearby friends’ extra weight would affect you more than the weight gain of buddies living across the country. The study found that neither happens.

Instead, the research provides us with new insight about the nature of human relationships, and how those we know influence our habits and social mores. It’s only fitting that Fowler, who has become one of the country’s leading experts on social networks, has had a hand in making these discoveries.

Despite all of the attention given to obesity, the importance of Fowler’s work had less to do with physical fitness and more to do with documenting how the actions of one person can, unintentionally, affect the decisions of those they know. In other words, it was a case study in social networks, with body weight being the variable Fowler used to track and measure how various components of these networks interact.

To begin understanding social networks, consider this simple example: Take a married man named Bob. If we know that Bob is sexually active, we also know, with a fairly high degree of certainty, that Bob’s spouse Mary is too. That one was pretty easy. But by studying other types of relationships between people, we should also be able to discern other, less intuitive, patterns in human behavior and attitudes. Once identified, we can turn these patterns into mathematical probabilities that allow us to make predictions about how one person’s decisions will influence everyone else in their social network.

To put it another way, our teachers have always told us about peer pressure. Fowler has a way to precisely measure its effects. And these measurements allow us to make predictions about people and their behavior by knowing certain facts about their friends.

A case in point is Fowler’s fat study, which he published with a colleague at the Harvard School of Medicine in last week’s edition of the New England Journal of Medicine. In 1971, researchers began working with about 5,000 people from a small town of Farmington, Mass., as part of a federal study of heart disease, measuring their height and weight over time. Over the course of three decades, the study expanded to cover the original cohorts’ spouses, kids and grandkids, all of whom told doctors the names of at least one friend. Because Farmington was a pretty small place, many of these friends were also included in the study.

Plugging all of this data into a statistical program allowed Fowler to model the various connections — social and familial — of the more than 12,000 people who took part in the Farmington study. The result provided a way to measure how changes in weight by one subject reverberated through the network.

What the researchers found, as you know by now, is that it appears that an overweight person sets a chain reaction, most probably by changing other people’s perception of what it means to be fat. Having a friend gain weight seems to lead to you gaining some too. When a really close friend gains weight, you gain more. But when a neighbor you barely know becomes pleasingly plump, you don’t change.

That social connections influence how you think and act is hardly news. The folks that started Alcoholics Anonymous had that figured out. Fowler’s contribution is to assign different mathematical probabilities to different types of social connections. If your spouse loses some weight, and your friend gains some, what would happen to you? The new study suggests you’d grow larger, because your friends appear to influence you more than your spouse or family members.

The insights of social network research are hardly limited to obesity. In another forthcoming paper, Fowler has developed a social map of Supreme Court decisions in order to discern the relative importance of each precedent. (In effect, Fowler created a MySpace network for each majority decisions, and then counted the number of friends each decision made.) In yet another study — most relevant to this correspondent — he also looked at the employment prospects for political science Ph.D. students at various universities.

There is, though, one important caveat about the obesity study: Understanding that the behavior of one person influences the behavior of another is hardly an invitation to discount the responsibility each of us has for our own actions. You may indeed grow more tolerant of being fat when those you know are large, but that doesn’t mean you give up your decision-making power, or the responsibility that comes with it. As your mother must’ve asked you, if your friends jumped off a bridge, would you do it too?

Instead, gaining new awareness about interrelationships should allow us to craft better public policies that make use of them. Take the example above about sexual activity. Understanding that it takes two people, AIDS activists in recent years have focused more attention on distributing condoms to African women, not just men, and teaching them how their own choices affect the transmission of the disease. These efforts have proven to be successful in slowing the rates of transmission.

Another UCSD political scientist, Gerald Mackie, has shown how the rise of new social conventions, in part through the use of organized peer pressure, helped end the widespread practice of foot-binding in China and has argued that similar efforts could end female genital mutilation in African countries.

Just as having overweight friends can lead to you being overweight, having skinny friends can prod you to lose weight. So by encouraging one person to live healthier, a public policy can actually have extensive effect by spreading the benefits throughout an entire social network.

Unfortunately, though political scientists have found ways to model social networks, they still haven’t pointed us to politically palatable policies that actually make that first person in the chain lose weight.

In the mean time, you might be better off joining a hiking club. (But remember, it’s not being a member of the club that will make you lose weight, it’s the peer pressure to hike.)

There is also another benefit to the new research. Next time I play hooky on a Friday, I’ll be able to tell my boss I came down with the fat bug.

Please contact Vladimir Kogan directly with your thoughts, ideas, personal stories or tips. Or send a letter to the editor.

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