title: Analyzing heterogeneity in the effects of physical activity in children on social network structure and peer selection dynamics.
abstract: BACKGROUND
  Social networks influence children and adolescents' physical activity. The focus of this paper is to examine the differences in the effects of physical activity on friendship selection, with eye to the implications on physical activity interventions for young children. Network interventions to increase physical activity are warranted but have not been conducted. Prior to implementing a network intervention in the field, it is important to understand potential heterogeneities in the effects that activity level have on network structure. In this study, the associations between activity level and cross sectional network structure, and activity level and change in network structure are assessed.
  
  
  METHODS
  We studied a real-world friendship network among 81 children (average age 7.96 years) who lived in low SES neighborhoods, attended public schools, and attended one of two structured aftercare programs, of which one has existed and the other was new. We used the exponential random graph model (ERGMs) and its longitudinal extension to evaluate the association between activity level and various demographic factors in having, forming, and dissolving friendship. Due to heterogeneity between the friendship networks within the aftercare programs, separate analyses were conducted for each network.
  
  
  RESULTS
  There was heterogeneity in the effect of physical activity on both cross sectional network structure and the formation and dissolution processes, both across time and between networks.
  
  
  CONCLUSIONS
  Network analysis could be used to assess the unique structure and dynamics of a social network before an intervention is implemented, so as to optimize the effects of the network intervention for increasing childhood physical activity. Additionally, if peer selection processes are changing within a network, a static network intervention strategy for childhood physical activity could become inefficient as the network evolves.
authors.affiliation: University of North Carolina at Chapel Hill, Wake Forest School of Medicine, Wake Forest School of Medicine.
authors.forename: Teague
authors.initials: T
authors.lastname: Henry
authors.affiliation: University of North Carolina at Chapel Hill, Wake Forest School of Medicine, Wake Forest School of Medicine.
authors.forename: Sabina B
authors.initials: SB
authors.lastname: Gesell
authors.affiliation: University of North Carolina at Chapel Hill, Wake Forest School of Medicine, Wake Forest School of Medicine.
authors.forename: Edward H
authors.initials: EH
authors.lastname: Ip
keywords: ERGM; STERGM; afterschool care program; childhood physical activity; children; established program; new network; physical activity; social network; social support