Are All Health Outcomes 'Contagious'? Detecting Implausible Social Network Effects in Acne, Height, and Headaches

Abstract:     
Background
Current methods used in medical literatures to estimate social network effects of health outcomes may be biased to find these effects, even if none actually exist.

Objective
To investigate whether we detect network effects for health outcomes that are unlikely to be subject to network phenomena.

Design
Our methods include statistical analysis now common in network studies such as logistic regression analysis with own and friend's lagged health status controlled. We extend the analysis by controlling for environmental confounders.

Setting
Sub-samples of the National Longitudinal Study of Adolescent Health (Add Health).

Participants
Between 4,300 and 5,400 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 were self-reported by respondents in 1994/5, 1995/6, and 2000/1.

Results
We find statistically significant network effects in the acquisition of acne, headaches and height. A friend's acne problems increased an individual's odds of acne problems (OR: 1.47, 95% confidence interval [0.93-2.33]). The likelihood that an individual has headaches also increases with the presence of a friend with headaches (OR: 1.62 [0.91-2.89]). An individual's height increases by 20% of his/her friends' height [0.15-0.26]. Each of these results was estimated using standard methodology found in several publications in leading medical journals such as the New England Journal of Medicine and other outlets. However, once environmental confounders are controlled, the results become uniformly smaller and insignificant.

Conclusions
Caution is suggested in attributing correlations in health outcomes of close friends to social network effects, especially when environmental confounders are not adequately controlled in the analysis.

Keywords: Peer Effects, Social Networks, Health

JEL Classifications: I12

Working Paper Series