Randy Newman was right

Studies of network contagion in health outcomes and behaviors (such as obesity and smoking) are all the rage these days. So it is interesting to read this paper in the current BMJ by Cohen-Cole and Fletcher that uses Add-Health data to establish some statistically significant but substantively rather implausible effects of just this sort:

Objective To investigate whether “network effects” can be detected for health outcomes that are unlikely to be subject to network phenomena. Design Statistical analysis common in network studies, such as logistic regression analysis, controlled for own and friend’s lagged health status. Analyses controlled for environmental confounders. Setting Subsamples of the National Longitudinal Study of Adolescent Health (Add Health). Participants 4300 to 5400 male and female adolescents who nominated a friend in the dataset and who were both longitudinally surveyed. Measurements Health outcomes, including headache severity, acne severity, and height self reported by respondents in 1994-5, 1995-6, and 2000-1. Results Significant network effects were observed in the acquisition of acne, headaches, and height. A friend’s acne problems increased an individual’s odds of acne problems (odds ratio 1.62, 95% confidence interval 0.91 to 2.89). The likelihood that an individual had headaches also increased with the presence of a friend with headaches (1.47, 0.93 to 2.33); and an individual’s height increased by 20% of his or her friend’s height (0.18, 0.15 to 0.26). Each of these results was estimated by using standard methods found in several publications. After adjustment for environmental confounders, however, the results become uniformly smaller and insignificant. Conclusions Researchers should be cautious in attributing correlations in health outcomes of close friends to social network effects, especially when environmental confounders are not adequately controlled for in the analysis.

(Via Cosma.)

Written by Kieran

December 11, 2008 at 5:32 am

7 Responses

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  1. “Researchers should be cautious in attributing correlations in health outcomes of close friends to social network effects, especially when environmental confounders are not adequately controlled for in the analysis.”

    Agreed. Though, that conclusion is a bit mis-leading: “environmental confounders” appear to also be wrapped up with nested individual-level effects, e.g., self-selection (the environment might naturally be endogenous to individuals). The article does discuss this, but I’m not sure that the respective levels here get teased out (well, having rich, longitudinal data like that of course makes this tough). A key issue is selection and node-effects, which rarely are controlled for, or the assumption is that the nodes are randomly assigned (studies often impute everything to the higher level — it’s just much sexier). Of course, every level probably contributes something to the overall effect — the question is which serves as the largest driver.



    December 11, 2008 at 6:12 am

  2. Yeah, even before this paper I’d gone from being cautiously optimistic about the network effects methodology used in the obesity and smoking papers cited in this paper to being skeptical. Although I would still be surprised if there weren’t nontrivial network effects on both obesity and smoking.



    December 11, 2008 at 9:40 am

  3. I’m just relieved that economists at the Fed have found *something* to occupy their time. I mean, not like there is anything exciting going on in the world of finance these days.


    Mrs. Smith

    December 11, 2008 at 12:07 pm

  4. Tks for the laugh, post read like a spoof until the “Conclusions”. Does the title refer to a song by Randy Newman’s song? If so which?
    @ Mrs. Smith:
    Isn’t it good to know that at least an economist at a Fed Bank can spot flaws in a methodology?


    l'oca s.

    December 11, 2008 at 12:24 pm

  5. @ K.
    don’t bother, i found the song, with a little help from my friends


    l'oca s.

    December 11, 2008 at 12:42 pm

  6. just to warn you kieran, my friend Johnny (you don’t know him), is sporting some nasty blackheads. you may want to get yourself some oxy-10.



    December 11, 2008 at 6:06 pm

  7. jsallaz: Post of the week! HA!



    December 18, 2008 at 3:34 pm

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