Universality properties of school-based preventive intervention targeted at cannabis use.

This study aims to examine the effect of school-based preventive intervention on cannabis use in Czech adolescents with different levels of risk factors and provide evidence of its universality. A randomized controlled prevention trial with six waves was conducted over a period of 33 months. We used a two-level logistic random-intercept model for panel data; we first looked at the statistical significance of the effect of the intervention on cannabis use, controlling for the characteristics of the children and time dummies. Then we analyzed the effects of the interactions between the intervention and the characteristics of the children on cannabis use and related it to the definition of universal preventive interventions. The setting for the study was in basic schools in the Czech Republic in the years 2007-2010. A total of 1,874 sixth-graders (mean age 11.82 years) who completed the baseline testing. According to our results, the prevention intervention was effective. We found all the selected characteristics of the children to be relevant in relation to cannabis use, except their relationships with their friends. We showed empirically that the intervention is universal in two dimensions for the selected characteristics of the children. First, all adolescents who undergo the intervention are expected to benefit. Second, with respect to the effect of the intervention on cannabis use, the total level of individual risk of cannabis use is superior to the composition of the risk factors in the individual risk profile. We present indicative evidence that the drug prevention intervention may be considered a true universal preventive intervention.