title: Physical activity and screen time in adolescents and their friends.
abstract: BACKGROUND
  Little is known about the actual physical activity and screen time behaviors of an adolescent's friends relative to the individual's behavior.
  
  
  OBJECTIVE
  To determine the associations between an adolescent's physical activity and screen time and his/her nominated friends' physical activity and screen time.
  
  
  METHODS
  Data were obtained from EAT 2010 (Eating and Activity Among Teens), a large cross-sectional study (n=2126) conducted in 20 middle schools and high schools in Minneapolis/St. Paul MN during the 2009-2010 academic year and analyzed during 2011. Each participant nominated up to six friends from a school roster, and data from those friends were obtained as part of the school-based data collection procedures. Physical activity and screen time were assessed with previously used and validated questionnaires. Generalized estimating equation models, stratified by gender, were used to assess associations between adolescents' physical activity and screen time and their friends' physical activity and screen time.
  
  
  RESULTS
  Physical activity for female adolescents was associated with their male and female friends' physical activity, including their male and female best friends (all p<0.05). Male adolescents' physical activity was associated with their female friends' physical activity (p<0.03). Female adolescents' screen time was associated with their male and female friends' screen time (p≤0.03), but not with that of their best friends. Male adolescents' screen time was associated with only their female friends' screen time (p=0.04).
  
  
  CONCLUSIONS
  The consistent association between female adolescents' physical activity and their friends' physical activity indicates a need to include peer effects on adolescent female physical activity in future intervention work.
authors.affiliation: Kinesiology Program, Curry School of Education, University of Virginia, Charlottesville, VA 22904-4407, USA. jrs2wq@virginia.edu
authors.forename: John R
authors.initials: JR
authors.lastname: Sirard
authors.forename: Meg
authors.initials: M
authors.lastname: Bruening
authors.forename: Melanie M
authors.initials: MM
authors.lastname: Wall
authors.forename: Marla E
authors.initials: ME
authors.lastname: Eisenberg
authors.forename: Sun K
authors.initials: SK
authors.lastname: Kim
authors.forename: Dianne
authors.initials: D
authors.lastname: Neumark-Sztainer
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D002648:Child; D003201:Computers / Q000706:statistics & numerical data*; D003430:Cross-Sectional Studies; D005260:Female; D033062:Friends; D006801:Humans; D008297:Male; D008910:Minnesota; D015233:Models, Statistical; D009043:Motor Activity / Q000502:physiology*; D012737:Sex Factors; D011795:Surveys and Questionnaires; D013690:Television / Q000706:statistics & numerical data*; D013997:Time Factors; D018910:Video Games / Q000706:statistics & numerical data*