title: Estimating the peer effect on youth overweight and inactivity using an intervention study.
abstract: BACKGROUND
  Understanding peer effect is potentially important for finding ways to combat the obesity epidemic. Nevertheless, it is not clear whether a peer effect exists because of the composition of the peer group, because the group members have similar, unobserved individual characteristics, or because of an endogenous effect.
  
  
  METHODS
  This issue is addressed here by using a unique longitudinal data set of 573 schoolchildren attending state schools in the Municipality of Aalborg, Denmark, during 2008-2010. To identify the spillover effect of a targeted intervention on peers, we use a difference-in-differences approach.
  
  
  RESULTS
  A targeted health intervention reduced body mass index (BMI) among overweight, inactive individuals and, more interestingly, that BMI among the nontreated peers was reduced by 1.04%.
  
  
  CONCLUSIONS
  The analysis suggests that individually targeted health intervention has a health benefit beyond the treated individual, which needs to be included when evaluating targeted policies aiming to combat childhood overweight and inactivity.
authors.affiliation: Department of Sociology and Social Work, Aalborg University, 5 Kroghstraede, Aalborg Oest 9220, Denmark. aqr@socsci.aau.dk.
authors.forename: Annette
authors.initials: A
authors.lastname: Quinto Romani
mesh_terms: D000293:Adolescent; D015992:Body Mass Index; D001837:Body Weights and Measures; D002648:Child; D003718:Denmark; D004032:Diet; D015444:Exercise; D005260:Female; D007722:Health Knowledge, Attitudes, Practice; D006293:Health Promotion / Q000458:organization & administration*; D006801:Humans; D008297:Male; D050177:Overweight / Q000523:psychology* / Q000628:therapy*; D010379:Peer Group; D010809:Physical Fitness; D012574:Schools; D057185:Sedentary Behavior; D012959:Socioeconomic Factors
keywords: difference-in-differences measure; experimental data; peer impact; targeted intervention