It has taken me several weeks to post this reply, which Dr. Christakis sent almost immediately after I sent him my email (see previous entry entitled "An Email to Dr. Nicholas Christakis"). During this time I've had the opportunity to learn and think more about Dr. Christakis' work, and was not shocked to discover that my knee jerk response to his NEJM article on the spread of obesity through social networks was premature. However, I was far from alone in this reaction.
He asked that I post his response verbatim:
Dear Ms. Gordon:
Thank you for your thoughtful and heartfelt note. I suppose the first thing I should say is that any study of the world will involve exceptions. Hence, even if (for the moment) we grant that our analyses are correct and, what is more, that our speculation about the cause of the apparent spread of obesity (namely, that there is a spread of norms regarding the acceptability of being overweight) is also correct, this would not mean that there might not be many cases, such as yours, that did not fit this rule.
Our general point is that, on average (albeit not in every case), people will be influenced by the weight status of those around them. In a way, your attempts to lose weight fit that bill, since you appear to have been (at least in part) influenced by the weight behaviors of those around you. An overlooked fact about our work is that we showed that both weight gain and weight loss spread in social networks; the reasons that weight gain predominates has to do with the other driving factors present in our environment that cause weight gain to begin with. In other words, something else starts the 'epidemic' and then the social network takes over, since networks have this interesting property of tending to magnify whatever they are seeded with (if you have the time, you might want to watch video # 2 at
I should also stress that we did not claim in our study to find 'the' cause of the obesity epidemic, but rather one contributing factor. While genes (as illustrated by a family history) no doubt play an important role in determining a person's body size, there is no way to blame the undeniable rise in average weight of Americans over the past three decades on genes; surely the explanatory factor is environmental since genes do not change on this time scale (although, incidentally, I do not preclude genetic change over longer time scales -- see: "Medicine Can Change Our Genes" at http://christakis.med.harvard.edu/pages/bmj.html ). These factors contributing to a rise in caloric intake and decline in calorie burning are numerous, and well known.
Finally, I should note that our work was much misunderstood in some quarters as somehow justifying prejudice, which I entirely renounce.
Again, thanks for taking the time to write.
Best,
Nicholas Christakis
What I learned from my correspondence with Dr. Christakis and a review of some of his vast trove of publications was that what had originally motivated him to study how feelings/perceptions spread through social networks was his work with terminally ill patients, which served as his initiation into clinical medicine. Through his interactions with these patients and their families, he understandably became concerned with the feelings of the family members and how it affected them and their social networks in turn.
I was surprised that as a Sociologist, Dr. Christakis would have been taken aback at the overwhelming attention received by his obesity study. Surely he must have been aware of the hair trigger emotions surrounding obesity in our society. It then occurred to me that perhaps, due to his initiation by fire into what must be one of the most difficult fields a physician can choose (end-of-life care), his attempt to approach the spreading of emotions through social networks through mathematics and statistics took him a step back from what must have been a very potent emotional experience. I felt that there was a certain detachment in thequantitative work involved in these analyses.
When I posited this to him, he explained:
As for the balance of qualitative and quantitative work: it is always a struggle. And while it is true that dealing directly with people who are suffering from terminal illness can be as demanding as it is rewarding, it is also true that the ostensibly antiseptic, quantitative analysis of death and dying can also be very dispiriting. Spending a day looking at survival curves of people, real people, who have died, often very quickly, can be almost as depressing. I spent a good many years making a quantitative study of end-of-life care, and how to improve it, as you can see from the following lists of papers:
again, thanks for writing.
best,
nicholas
Dr. Christakis is not primarily studying the "obesity epidemic" but rather how social networks work.
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