Social Dynamics in Obesity: A Decomposition of the Obesity Epidemic Paolo Nicola Barbieri⇤† May 14, 2014 Abstract This paper examines the influence of social factors on weight gain and obesity. We develop a concept of social norm related to the social evolution of obesity developed through shared experiences in a common social environment. When overweight is common it can represents a prominent feature of the social environment and an important contributor to weight-related norms influencing individual social identity. We prove that our measure of such social component are significantly influencing individual obesity. We then take advantage of a markedly significant between di↵erence in obesity in England between the years 2002 and 2010 to undertake two decomposition analysis. The decompositions are based from Health Survey for England (HSE) cross-sectional data. Using a (linear) Blinder-Oaxaca decomposition we have attempted to isolate the influence of the exogenous social norm. With a (non-linear) Fairlie’s decomposition we attempted to quantify the influence of such social norms. Our findings suggest that the when we do not include the social norms our estimates explain 32% of the obesity gap. However when we include the social norms our estimates explain between 35% to 70% of the obesity gap wiping out the e↵ect of all other variables. These results suggest that body weight depends on social norms a↵ecting individual’s health production, and that such e↵ect increased over time. JEL-Classification: D91, I10, I12, I18, Z13 Keywords: Obesity, England, decomposition, non-linear decomposition, social norm ”The social aspects of obesity may have a [social] multiplier e↵ect on the growth of obesity. When obesity is relatively rare, it is considered abnormal and repulsive, and this negative response helps to keep it in check. As obesity begins to rise, the negative image of obesity becomes less intense because obesity is now more common” Philipson and Posner, JEL (2008) ⇤ I am thankful to Alessandro Saia, Francesca Barigozzi, Giulio Zanella, Franco Sassi, Marion Devaux, Davide Dragone for insightful comments. † Corresponding author. University of Bologna Italy, Department of Economics, P.zza Scaravilli 2 40126 - Bologna (Italy) E-mail address: [email protected]. 1