title: Diffusion of Intervention Effects: The Impact of a Family-Based Substance Use Prevention Program on Friends of Participants.
abstract: OBJECTIVE
  We tested whether effects of the Strengthening Families Program for Youth 10-14 (SFP10-14) diffused from intervention participants to their friends. We also tested which program effects on participants accounted for diffusion.
  
  
  METHODS
  Data are from 5,449 students (51% female; mean initial age = 12.3 years) in the PROmoting School-community-university Partnerships to Enhance Resilience community intervention trial (2001-2006) who did not participate in SFP10-14 (i.e., nonparticipants). At each of five waves, students identified up to seven friends and self-reported past month drunkenness and cigarette use, substance use attitudes, parenting practices, and unsupervised time spent with friends. We computed two measures of indirect exposure to SFP10-14: total number of SFP-attending friends at each wave and cumulative proportion of SFP-attending friends averaged across the current and all previous post-intervention waves.
  
  
  RESULTS
  Three years post-intervention, the odds of getting drunk (odds ratio = 1.4) and using cigarettes (odds ratio = 2.7) were higher among nonparticipants with zero SFP-attending friends compared with nonparticipants with three or more SFP-attending friends. Multilevel analyses also provided evidence of diffusion: nonparticipants with a higher cumulative proportion of SFP-attending friends at a given wave were less likely than their peers to use drugs at that wave. Effects from SFP10-14 primarily diffused through friendship networks by reducing the amount of unstructured socializing (unsupervised time that nonparticipants spent with friends), changing friends' substance use attitudes, and then changing nonparticipants' own substance use attitudes.
  
  
  CONCLUSIONS
  Program developers should consider and test how interventions may facilitate diffusion to extend program reach and promote program sustainability.
authors.affiliation: Department of Public Health Education, University of North Carolina at Greensboro, Greensboro, North Carolina. Electronic address: klruliso@uncg.edu.
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Rulison
authors.affiliation: The Prevention Research Center, The Pennsylvania State University, University Park, Pennsylvania.
authors.forename: Mark
authors.initials: M
authors.lastname: Feinberg
authors.affiliation: Department of Human Development and Family Studies, Pennsylvania State University, University Park, Pennsylvania.
authors.forename: Scott D
authors.initials: SD
authors.lastname: Gest
authors.affiliation: Crime, Law and Justice Program, Department of Sociology, Pennsylvania State University, University Park, Pennsylvania.
authors.forename: D Wayne
authors.initials: DW
authors.lastname: Osgood
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior / Q000523:psychology*; D000428:Alcohol Drinking / Q000517:prevention & control* / Q000523:psychology; D002648:Child; D005260:Female; D033062:Friends / Q000523:psychology*; D006293:Health Promotion / Q000379:methods / Q000706:statistics & numerical data*; D006801:Humans; D008019:Life Style; D008297:Male; D010379:Peer Group; D011314:Preventive Health Services / Q000379:methods*; D012309:Risk-Taking; D012907:Smoking / Q000523:psychology; D000074606:Smoking Prevention
keywords: Alcohol use; Cigarette use; Diffusion; Friendship; Intervention effects; Social networks