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How the ‘friendship paradox’ might help predict flu outbreaks

How central are you to your network of friends?

If your friends consider you a trendsetter, you may be ahead of them in more ways than they — or you — think. You may also be among the first to catch the flu this season.

For a study published earlier this fall in the medical journal PLos One has found that popular people — those who are at the center of their social networks — are more likely to become infected with the flu early in an epidemic.

OK. This may not be earth-shattering news to you. (Of course, popular people get the flu earlier. They’re in contact with more people.) But it does have some interesting ramifications. The Centers for Disease Control and Prevention (CDC) and other public health officials are generally about two weeks behind in identifying the start of an epidemic. The social network barometer used in this study — the so-called friendship paradox — might give those officials a tool to detect contagious outbreaks much earlier, before they happen in the general population and when preventive actions might help keep the outbreak from spreading too widely.

What exactly is the friendship paradox? First described in 1991 (long, long before the rise of Facebook and other social media), it essentially says that your friends are probably more popular than you are. (Sorry.) Or, to be more specific, they have more friends than you do. Furthermore, when asked to name a couple of your friends, you’re more likely to name individuals who rank higher on the social strata (in terms of popularity) than you.

In the PLos One study, researchers James Fowler of the University of California, San Diego and Dr. Nicholas Christakis of Harvard University set out to determine if the friendship paradox could be used to predict a flu outbreak. They randomly selected 319 Harvard undergraduates who responded to an e-mail seeking volunteers. Asked to name three close friends, those undergrads turned up another 425 names.

Both of these groups (“random” and “friends”) were carefully tracked during last year’s flu season. Members of the friends group were diagnosed with the flu an average of 13.9 days sooner than those in the randomly chosen group (in other words, in the general population). They were also diagnosed an average of 46 days before the peak of the flu epidemic (as determined by other means).

“If you want a crystal ball for finding out which parts of the country are going to get the flu first, then this may be the most effective method we have now,” said Fowler in a Harvard University press release. “Currently used methods are based on statistics that lag the real world — or, at best, are contemporaneous with it. We show a way you can get ahead of an epidemic of flu, or potentially anything else that spreads in networks.”

And “anything else” really means just about anything, including drug use, the next “must-have” gadget or toy, fashion styles and, yes, even the emergence of new political ideas.

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