title: Examining social norm impacts on obesity and eating behaviors among US school children based on agent-based model.
abstract: BACKGROUND
  Although the importance of social norms in affecting health behaviors is widely recognized, the current understanding of the social norm effects on obesity is limited due to data and methodology limitations. This study aims to use nontraditional innovative systems methods to examine: a) the effects of social norms on school children's BMI growth and fruit and vegetable (FV) consumption, and b) the effects of misperceptions of social norms on US children's BMI growth.
  
  
  METHODS
  We built an agent-based model (ABM) in a utility maximization framework and parameterized the model based on empirical longitudinal data collected in a US nationally representative study, the Early Childhood Longitudinal Study - Kindergarten Cohort (ECLS-K), to test potential mechanisms of social norm affecting children's BMI growth and FV consumption.
  
  
  RESULTS
  Intraclass correlation coefficients (ICC) for BMI were 0.064-0.065, suggesting that children's BMI were similar within each school. The correlation between observed and ABM-predicted BMI was 0.87, indicating the validity of our ABM. Our simulations suggested the follow-the-average social norm acts as an endogenous stabilizer, which automatically adjusts positive and negative deviance of an individual's BMI from the group mean of a social network. One unit of BMI below the social average may lead to 0.025 unit increase in BMI per year for each child; asymmetrically, one unit of BMI above the social average, may only cause 0.015 unit of BMI reduction. Gender difference was apparent. Social norms have less impact on weight reduction among girls, and a greater impact promoting weight increase among boys. Our simulation also showed misperception of the social norm would push up the mean BMI and cause the distribution to be more skewed to the left. Our simulation results did not provide strong support for the role of social norms on FV consumption.
  
  
  CONCLUSIONS
  Social norm influences US children's BMI growth. High obesity prevalence will lead to a continuous increase in children's BMI due to increased socially acceptable mean BMI. Interventions promoting healthy body image and desirable socially acceptable BMI should be implemented to control childhood obesity epidemic.
authors.affiliation: Department of Epidemiology and Environmental Health, School of Public Health and Health Professions, University at Buffalo, State University of New York, Buffalo, NY, USA. youfawan@buffalo.edu.
authors.forename: Youfa
authors.initials: Y
authors.lastname: Wang
authors.forename: Hong
authors.initials: H
authors.lastname: Xue
authors.forename: Hsin-jen
authors.initials: HJ
authors.lastname: Chen
authors.forename: Takeru
authors.initials: T
authors.lastname: Igusa
mesh_terms: D001828:Body Image; D015992:Body Mass Index; D002648:Child; D005247:Feeding Behavior; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008962:Models, Theoretical; D063766:Pediatric Obesity / Q000523:psychology*; D012574:Schools; D066262:Social Norms; D014481:United States