Is Obesity Contagious? Social Networks vs. Environmental Factors in the Obesity Epidemic

This note's aim is to investigate the sensitivity of Christakis and Fowler's claim [Christakis, N., Fowler, J., 2007. The spread of obesity in a large social network over 32 years. The New England Journal of Medicine 357, 370-379] that obesity has spread through social networks. It is well known in the economics literature that failure to include contextual effects can lead to spurious inference on "social network effects." We replicate the NEJM results using their specification and a complementary dataset. We find that point estimates of the "social network effect" are reduced and become statistically indistinguishable from zero once standard econometric techniques are implemented. We further note the presence of estimation bias resulting from use of an incorrectly specified dynamic model.

[1]  Lung-fei Lee,et al.  Identification and estimation of econometric models with group interactions, contextual factors and fixed effects , 2007 .

[2]  Bernard Fortin,et al.  Identification of Peer Effects through Social Networks , 2007, SSRN Electronic Journal.

[3]  Mary A. Burke,et al.  Social Dynamics of Obesity , 2006 .

[4]  K. Flegal,et al.  Prevalence of overweight and obesity among US children, adolescents, and adults, 1999-2002. , 2004, JAMA.

[5]  Jesse M. Shapiro,et al.  Why Have Americans Become More Obese? , 2003 .

[6]  K. Flegal,et al.  Prevalence and trends in obesity among US adults, 1999-2000. , 2002, JAMA.

[7]  M. Grossman,et al.  An Economic Analysis of Adult Obesity: Results from the Behavioral Risk Factor Surveillance System , 2002, Journal of health economics.

[8]  L. Cupples,et al.  Genetic variability of adult body mass index: a longitudinal assessment in framingham families. , 2002, Obesity research.

[9]  R. Posner,et al.  The Long-Run Growth in Obesity as a Function of Technological Change , 1999, Perspectives in biology and medicine.

[10]  C. Manski.  Identification of Endogenous Social Effects: The Reflection Problem , 1993 .

[11]  G. Mcclearn,et al.  The body-mass index of twins who have been reared apart. , 1990, The New England journal of medicine.

[12]  J. Stockman.  The Spread of Obesity in a Large Social Network over 32 Years , 2009 .

[13]  J. Kagel,et al.  Dynamic Discrete Choice Models with Lagged Social Interactions: with an Application to a Signaling Game Experiment , 2006 .

[14]  A. Emery,et al.  Genetic variability , 1980, Nature.