Monday, June 20, 2011

Obesity is contagious, or is it? A sober second look at obesity and social networks.

Right off the top let me say I'm not well versed enough in statistics to know who's right.

On one side of the fence are the findings of Christakis and Fowler, famously published in the New England Journal of Medicine that posited obesity is socially contagious. Non-statistically, their paper didn't sit right with me, but as far as stats go, I'm no maven.

On the other side of the fence is a new paper published by Russel Lyons who posits that Christakis' and Fowler's work is a great example of statistical illiteracy, and that the conclusion drawn from their data, that obesity is socially contagious, is severely flawed and can't be made.

Lyons' paper, in a nutshell, gives statistical meat to my gut's firm belief - that shared environments and self-selection may well be explanatory for the clustering of obesity in social networks. That folks whose lifestyles may be more conducive to obesity, may well gravitate towards one another, and/or that people living in geographically/socially similar environments, environments that may contribute to the risk of obesity, together share increased risks and outcomes.

Statistical arguments aside (frankly they're way over my head and I couldn't begin to venture a guess who's right and who's wrong), what was most fascinating to me was Lyons' discussion of his paper's publication.

If Lyons' hypothesis is correct, his paper's a big deal. It refutes one of the most widely publicized studies of the decade, one that's translated itself into millions of dollars of grants, countless news stories, and even a book that's been published in 20 different languages.

So what happened when he tried to publish it?

The New England Journal of Medicine and the BMJ rejected it outright, without peer review. JAMA, the Lancet and the Proc. Nat. Acad. Sci. all rejected it next, this time because they have policies of not publishing critiques of articles they themselves didn't publish.

Next Lyons submitted his paper to a statistics journal. The journal, Stat. Sci., did send it out for peer review. 2 of the 3 referees recommended publication without revision, and the 3rd, clearly not an obesity researcher, stated that while they agreed with Lyons' conclusions, that the subject was not important enough to warrant publication. Stat. Sci.'s editors agreed with reviewer number 3, and rejected the paper.

Eventually Lyons' work was published in the journal Statistics, Politics, and Policy, whose impact factor rates at 0.857. Contrast that with the impact factor of 50 that the New England Journal of Medicine enjoys.

The entire experience has led Lyons to use his paper as a call to action to establish a journal whose subject matter is made up solely of study critiques. Were such a journal available, it would create a venue for publication of important criticisms, further protect the public from bad statistical analyses, and potentially serve as an incentive for researchers to double check their work.

All in all, even if you're not a statistician, Lyons' paper is worth a sober read and reflection, and here's something else to chew on - the journalists who were originally all over Christakis' and Fowler's work? I'd bet every last penny I've got that not a single one of them were skilled enough in statistical analysis to analyze it. Really, why should they have been? They're journalists, not statisticians. No, instead they smelled a good story, and ran with it. Those same journalists who shouted from the rooftops that obesity's contagious? I'm betting the vast majority of them are going to be silent on this one, yet wouldn't re-reporting be the socially responsible, ethical, and journalistic right thing to do?

Now I know that plenty of reporters read this blog. Would love to hear from you. Am I off base?

Lyons, R. (2011). The Spread of Evidence-Poor Medicine via Flawed Social-Network Analysis Statistics, Politics, and Policy, 2 (1) DOI: 10.2202/2151-7509.1024

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  1. Thanks for posting this - I have countered with the Lyons study a couple of times when people have brought up the "obesity is contagious" study. As for journalists, if they are not lazy, they can tell a more balanced story without needing to know statistics, but you know that already. Too bad health reporters don't.

  2. Oh sorry - I meant, that I have used the BMJ article! Have a good day.

  3. I'm an editor and I'll weigh in. I don't allow health stories in my magazine unless they're written by someone with a science background and a sceptical attitude. The reality for most publications, though, is that stories that are seen to be about lifestyle issues are usually sent to the lifestyle sections, not the science/health sections and are written up by people who don't understand the issues involved. This can lead to the scientifically literate journos tearing their hair out.

  4. I've always thought that it would be ideal if everybody understood some basic statistics but when you see conflicting studies like these where the statistics used are way beyond me, anyway, what do you do. Has the Cochrane Collaboration addressed these social network studies.

  5. I think they have a flaw in the underlying assumption. Anyone who had a grandmother who's was known for "yets, yets" or eat, eat, known that family relationships with respect to food are not bidirectional, but unidirectional, old to young. We simply learned bad habits by listening, too much sugar, grain, chocolate, oils, to much good food. Once the habit is formed, we need to beat the habit, as well as the addiction, hedonic response, the excess insulin, mental issues, and our lust for food in general.

    Tie: A connection between two nodes that can be either one-way (directed)
    or two-way (bilateral). In this study, all family ties (e.g., between siblings
    and parents) as well as marital ties are bilateral, but friendship ties are directional
    since a subject may identify someone as a friend who does not
    necessarily identify that person as a friend in return.

  6. Isn't there a journal with the exclusive subject of obesity?
    10 seconds of Google gave me this:

    I wonder if Russel Lyons tried submitting to this journal?

  7. My master's is in journalism. I agree with the late Molly Ivins. Journalists are mostly lazy. Many contemporary journalists simply report explosive points of view. If they get one person to say something contraversial, then find another person to counter it with something equally contraversial, then they think they've done their job. Story done. Getting to some sort of truth? Doing fact checking? Fuggetaboutit!

    Ivins said that if a contemporary journalist were to cover WWII, then he might get a concentration camp survivor's sound bite on the terrors she'd experienced in captivity, followed by one of Hitler's friends talking about what a peach of a guy he is, when you get to know him.

  8. Anonymous12:25 am

    Are food blogs social networks?

  9. Anonymous12:27 am


    I've worked in msm all my life. I've never heard journalists called "journos". Hahahahaha.

    We're reporters or writers.

    So what was it, again, you wanted to tell us about expertise forming knowledge?

  10. This is a compelling and disturbing development. I emailed Gary Schwitzer (Medscape's HealthNewsReview investigative journalist/professor blogger) and Pia Christensen at the Covering Health blog of the Association of Healthcare Journalists and asked them to respond to your post.

  11. Wow! That was fast! Gary Schwitzer emailed me that he's traveling overseas w/ limited wifi and will investigate when he has better access. And Pia Christensen has already blogged a response.

  12. Thanks for spreading the word aek.

    Looking forward to hearing what their journalists think they should or shouldn't be doing regarding the story.

  13. Anonymous10:22 am

    Journos as a term is used all the time in the UK and Australia.

  14. Anonymous9:45 pm

    Am I the only one who knows how to read between to lines. Obesity is not contagious LITERALLY but, both good and bad habits are. Especially if there are no conflicting beliefs.

  15. Anonymous10:23 am

    @anonymous 12:27, careful, your insularity is showing