title: Universal intervention as a protective shield against exposure to substance use: long-term outcomes and public health significance.
abstract: OBJECTIVE
  We examined universal preventive intervention effects on adolescents' exposure to opportunities for substance use and on illicit substance use in the long term.
  
  
  METHODS
  Public schools (N = 22) were randomly assigned to the Iowa Strengthening Families Program (ISFP) or a control condition. We used odds ratio (OR) calculations and structural modeling to test the effects of the ISFP in the 6th grade on exposure to substance use across adolescence, as well as on 12th-grade illicit substance use occurring via reductions in exposure.
  
  
  RESULTS
  The ISFP was associated with reduced exposure to illicit substance use (1.25 < or = OR < or = 2.37) that was, in turn, associated with reduced 12th-grade substance use (2.87 < or = OR < or = 6.35). The ISFP also reduced the rate of increase in exposure across adolescence (B = -0.37; P < .001), which was associated with the likelihood of 12th-grade illicit substance use (B = 0.30; P = .021), with a significant indirect effect (B = -0.11; P = .048).
  
  
  CONCLUSIONS
  The ISFP in the 6th grade reduced substance use through a "protective shield" of reduced exposure. The relative reduction rate was 49%, which suggests that universal prevention shields can contribute to significant reductions in illicit substance use among adolescents.
authors.affiliation: Partnerships in Prevention Science Institute, ISU Research Park, Building 2, Suite 2500, 2625 North Loop Drive, Iowa State University, Ames, Iowa 50010, USA. rlspoth@iastate.edu
authors.forename: Richard
authors.initials: R
authors.lastname: Spoth
authors.forename: Max
authors.initials: M
authors.lastname: Guyll
authors.forename: Chungyeol
authors.initials: C
authors.lastname: Shin
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D016022:Case-Control Studies; D002648:Child; D003159:Community-Institutional Relations; D005190:Family; D006293:Health Promotion; D006801:Humans; D007484:Iowa; D016017:Odds Ratio; D010379:Peer Group; D012933:Social Identification; D019966:Substance-Related Disorders / Q000453:epidemiology / Q000517:prevention & control*