you may have noticed something a bit different about this post’s title. it’s in title case. that’s because carol harnett—author, speaker and trendspotter—wrote it. after the new york times ran an article that calls into question christakis’ and fowlers’ findings that health behavior is contagious, i asked carol to share her thoughts on what it meant. and i “let” her write the entire thing in traditional case.
One of the most powerful classes I took in graduate school was called, “How to Lie with Statistics.” You must love a stats professor who knows how to market his curriculum.
No, he didn’t really teach us how to lie. Our instructor taught us how to discern – good from bad design, statistical significance from insignificance, and proper from flawed statistical conclusions.
That’s why, when the journal, Statistics, Politics, and Policy published Russell Lyon’s paper, The Spread of Evidence-Poor Medicine via Flawed Social-Network Analysis in May 2011, I was immediately captivated.
Okay, not immediately. I have geek-like tendencies, but I don’t subscribe to this journal.
I do, however, have a statistics Twitter list. And, within a couple of weeks of the Lyons paper hitting the proverbial newsstand, my Twitter list was chock-full of posts about the statistical flaws surrounding the research of Nicholas Christakis and James Fowler on the social contagion of obesity, smoking, happiness and loneliness.
So, in laymen’s terms, what’s all the fuss about?
Essentially, Christakis and Fowler propose that our body weight, tendency to smoke cigarettes and states of happiness and loneliness are spread—like a virus—by up to three degrees of friends (friends, friends of friends, and friends of friends of friends, i.e., the next-door neighbor of your best friend’s college roommate).
The researchers assert that this extended friends’ network causes these personality traits to multiply through a process similar to infectious disease transmission. And, that this transmission is not limited by geographic location or where these people live.
Causality is a pretty big statement—much different than saying these conditions are associated with your friends and their networks.
What’s the difference between causality and association? Let’s use some examples.
When we’re talking about health, rarely do we conclusively find that one thing causes another. Hand washing, as a way to reduce the spread of infectious disease, is an exception. It is widely accepted and supported by research that washing your hands cuts down the spread of infection.
Most of everything else we promote about healthy behaviors is an association. For example, obesity is associated with a greater risk for heart disease and cancer. However, obesity alone does not cause heart disease or cancer.
To get to this idea that obesity spreads like a virus, Christakis and Fowler had to rule out two concepts: homophily and shared environment.
Homophily boils down to one of my grandmother’s favorite sayings, “Show me your friends and I’ll tell you who you are.” In other words, we tend to associate with people who look like us and act like us.
Shared environment is exactly what it sounds like. We live in the same or similar places and those environments influence our personality traits and choices.
According to a growing list of statisticians who support Lyons’ work, Christakis and Fowler’s statistical techniques, which allowed them to rule out the influence of where we live and choosing friends who are like us, were greatly flawed.
Their errors, according to Lyons, are summed up as follows:
“1. [Christakis and Fowler] use statistical models that contradict their data, as well as their conclusions.
“2. Even if one accepts [Christakis and Fowler’s] statistical models and tests, [Christakis and Fowler] interpret the results incorrectly.”
The bottom line? Statisticians say that Christakis and Fowler cannot make the statements they made using the statistical methods they chose. They also believe that their mistake was inadvertent, not intentional.
So, is there anything you can take away from the great debate about the validity of Christakis and Fowler’s research?
First, the people we hang out with and where we live, work and play influence our choices and behaviors.
Second, no one is saying that social contagion doesn’t exist and have influence. Heck, the only reason Lyons’ paper made it beyond the statistics world to the New York Times was because people spread it on Twitter.
As Dave Johns wrote in Slate, “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.”
Third, use discernment when reading research—even in venerable journals like the New England Journal of Medicine and the British Medical Journal. It’s no one’s intention to lie with statistics, but it’s easy to make mistakes.