But the media world does not, and for the past few years Christakis and Fowler have been happy to race ahead of peer review and feed the news borg with interviews on tasty topics like contagious divorce. The publicity has helped them achieve scientific stardom. They speak regularly to enthusiastic crowds about their network studies and their 2009 book Connected, which has been translated into Chinese, Croatian, Dutch, German, Greek, Hebrew, Hungarian, Indonesian, Japanese, Korean, Polish, Portuguese, Romanian, Russian, Spanish, Swedish, Thai, Turkish and—cheerio!—British English.
Despite their omnipresence, they have argued that their media appearances should be considered distinct from their science. In their draft statistical paper they write, "We do not think that short remarks we have made to reporters (or even on comedy shows, which one critic took us to task for) should be used to evaluate our findings." Yes, I did take Fowler to task for an interview he gave to Stephen Colbert, during which he claimed to have lost a few pounds so as to avoid infecting those around him with excess flab. Yet I only learned of the Colbert appearance after interviewing economist Charles Manski, a lion in the world of quantitative social science, who called it the "low point" for him in the theater surrounding the flawed studies. The problem was not that Fowler was dispensing with scientific precision for a lay audience; the problem was that he was giving unfounded health advice on national television, Manski said. (On the more difficult scientific matter of whether the force field of comedic "truthiness" that envelopes Stephen Colbert also protects his guests, my sense is no, but that question goes beyond the scope of this article.)
Although the social-contagion studies have been media hits, there has been less demand for the debunking stories in the science news marketplace. After the Lyons study was published, a few health and media blogs took note and began to ask why more journalists weren't covering it. People are more interested in reading about new findings than a refutation of those findings, explained Forbes science writer Matthew Herper as the discussion moved to Twitter.
The scientific establishment has the same problem: Outlets for critiques are relatively few and not highly regarded. Consider that Lyons' paper appeared in a brand-new and hence totally obscure journal. Christakis and Fowler's work, by contrast, has appeared in some of the most prestigious medical journals in the world, including the New England Journal of Medicine and the British Medical Journal. In fact, Lyons tried submitting his article to both those places, but it was rejected without peer review. NEJM did not offer a reason; BMJ suggested his piece was better off in a "specialist journal." (Ironically, in 2010 the latter published an editorial titled "Inadequate post-publication review of medical research.") He also tried other top journals, but, according to Lyons, they were not interested because they do not publish critiques of articles they didn't originally publish. Critiques lack the same kind of novelty as original studies and they are necessarily tedious and impolite. (Indeed, Lyons' paper is not long on politeness, which probably hurt his chances.)
So is obesity contagious? What about happiness and divorce and poor sleep? One irony of the contagion battles is that even if their methods are suspect Christakis and Fowler are obviously correct that peer influence exists and that it may be even more important than we realize. As Cosma Shalizi put it on his blog last week, "there is a reason that my Pittsburgh-raised neighbors say 'yard' differently than my friends from Cambridge, and it's not the difference between drinking from the Monongahela rather than the Charles." The very idea of contagion and connectedness seems to embody the spirit of today, from the upswell of support for a young, black Chicago politician to the Facebook-driven revolutions of the Middle East.
But just because contagion is important in one context doesn't mean something like obesity spreads like a virus—much less one that can infect someone as remote from you as your son's best friend's mother. (For the record, I and my best friend's mother will eat our hats if it turns out to be true, as Christakis and Fowler claim, that loneliness is infectious, too.) Yes, we influence each other all the time, in how we talk and how we dress and what kinds of screwball videos we watch on the Internet. But careful studies of our social networks reveal what may be a more powerful and pervasive effect: We tend to form ties with the people who are most like us to begin with. The mother who blames her son's boozebag friends for his wild behavior must face up to the fact that he prefers the fast crowd in the first place. We are all connected, yes, but the way those links get made could be the most important part of the story.