title: Detecting implausible social network effects in acne, height, and headaches: longitudinal analysis.
abstract: OBJECTIVE
  To investigate whether "network effects" can be detected for health outcomes that are unlikely to be subject to network phenomena.
  
  
  METHODS
  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.
  
  
  METHODS
  Subsamples of the National Longitudinal Study of Adolescent Health (Add Health).
  
  
  METHODS
  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.
authors.affiliation: Federal Reserve Bank of Boston, 600 Atlantic Avenue, Boston, MA 02210, USA.
authors.forename: Ethan
authors.initials: E
authors.lastname: Cohen-Cole
authors.forename: Jason M
authors.initials: JM
authors.lastname: Fletcher
mesh_terms: D000152:Acne Vulgaris / Q000523:psychology*; D000293:Adolescent; D000328:Adult; D001827:Body Height; D004522:Educational Status; D004812:Epidemiologic Methods; D005260:Female; D020773:Headache Disorders / Q000523:psychology*; D006304:Health Status; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D012944:Social Support; D014481:United States; D055815:Young Adult