title: Effects of the X:IT smoking intervention: a school-based cluster randomized trial.
abstract: BACKGROUND
  Uptake of smoking in adolescence is still of major public health concern. Evaluations of school-based programmes for smoking prevention show mixed results. The aim of this study was to examine the effect of X:IT, a multi-component school-based programme to prevent adolescent smoking.
  
  
  METHODS
  Data from a Danish cluster randomized trial included 4041 year-7 students (mean age: 12.5) from 51 intervention and 43 control schools. Outcome measure 'current smoking' was dichotomized into smoking daily, weekly, monthly or more seldom vs do not smoke. Analyses were adjusted for baseline covariates: sex, family socioeconomic position (SEP), best friend's smoking and parental smoking. We performed multilevel, logistic regression analyses of available cases and intention-to-treat (ITT) analyses, replacing missing outcome values by multiple imputation.
  
  
  RESULTS
  At baseline, 4.7% and 6.8% of the students at the intervention and the control schools smoked, respectively. After 1 year of the intervention, the prevalence was 7.9% and 10.7%, respectively. At follow-up, 553 students (13.7%) did not answer the question on smoking. Available case analyses: crude odds ratios (OR) for smoking at intervention schools compared with control schools: 0.65 (0.48-0.88) and adjusted: 0.70 (0.47-1.04). ITT analyses: crude OR for smoking at intervention schools compared with control schools: 0.67 (0.50-0.89) and adjusted: 0.61 (0.45-0.82).
  
  
  CONCLUSIONS
  Students at intervention schools had a lower risk of smoking after a year of intervention in year 7. This multi-component intervention involving educational, parental and context-related intervention components seems to be efficient in lowering or postponing smoking uptake in Danish adolescents.
authors.affiliation: National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark anan@niph.dk.
authors.forename: Anette
authors.initials: A
authors.lastname: Andersen
authors.affiliation: National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
authors.forename: Rikker
authors.initials: R
authors.lastname: Krølner
authors.affiliation: National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
authors.forename: Lotus Sofie
authors.initials: LS
authors.lastname: Bast
authors.affiliation: National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
authors.forename: Lau Caspar
authors.initials: LC
authors.lastname: Thygesen
authors.affiliation: National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
authors.forename: Pernille
authors.initials: P
authors.lastname: Due
mesh_terms: D000293:Adolescent; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006293:Health Promotion / Q000379:methods*; D006801:Humans; D008297:Male; D016017:Odds Ratio; D010290:Parents; D015995:Prevalence; D012572:School Health Services; D012574:Schools; D061845:Smoke-Free Policy; D012907:Smoking / Q000453:epidemiology; D000074606:Smoking Prevention
keywords: Smoking prevention; adolescents; cluster randomized controlled trial; intervention study; multilevel analyses; multiple imputation