title: Cannabis use in children with individualized risk profiles: Predicting the effect of universal prevention intervention.
abstract: OBJECTIVE
  To study the effect of a universal prevention intervention targeting cannabis use in individual children with different risk profiles.
  
  
  METHODS
  A school-based randomized controlled prevention trial was conducted over a period of 33 months (n=1874 sixth-graders, baseline mean age 11.82). We used a two-level random intercept logistic model for panel data to predict the probabilities of cannabis use for each child. Specifically, we used eight risk/protective factors to characterize each child and then predicted two probabilities of cannabis use for each child if the child had the intervention or not. Using the two probabilities, we calculated the absolute and relative effect of the intervention for each child. According to the two probabilities, we also divided the sample into a low-risk group (the quarter of the children with the lowest probabilities), a moderate-risk group, and a high-risk group (the quarter of the children with the highest probabilities) and showed the average effect of the intervention on these groups.
  
  
  RESULTS
  The differences between the intervention group and the control group were statistically significant in each risk group. The average predicted probabilities of cannabis use for a child from the low-risk group were 4.3% if the child had the intervention and 6.53% if no intervention was provided. The corresponding probabilities for a child from the moderate-risk group were 10.91% and 15.34% and for a child from the high-risk group 25.51% and 32.61%. School grades, thoughts of hurting oneself, and breaking the rules were the three most important factors distinguishing high-risk and low-risk children.
  
  
  CONCLUSIONS
  We predicted the effect of the intervention on individual children, characterized by their risk/protective factors. The predicted absolute effect and relative effect of any intervention for any selected risk/protective profile of a given child may be utilized in both prevention practice and research.
authors.affiliation: Department of Addictology, First Faculty of Medicine, Charles University in Prague and General University Hospital in Prague, Czech Republic.
authors.forename: Michal
authors.initials: M
authors.lastname: Miovský
authors.affiliation: Department of Addictology, First Faculty of Medicine, Charles University in Prague and General University Hospital in Prague, Czech Republic; Institute for Research and Development in Education, Faculty of Education, Charles University in Prague, Czech Republic.
authors.forename: Hana
authors.initials: H
authors.lastname: Vonkova
authors.affiliation: Department of Addictology, First Faculty of Medicine, Charles University in Prague and General University Hospital in Prague, Czech Republic.
authors.forename: Lenka
authors.initials: L
authors.lastname: Čablová
authors.affiliation: Department of Addictology, First Faculty of Medicine, Charles University in Prague and General University Hospital in Prague, Czech Republic. Electronic address: gabrhelik@adiktologie.cz.
authors.forename: Roman
authors.initials: R
authors.lastname: Gabrhelík
mesh_terms: D002648:Child; D018153:Czech Republic / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008385:Marijuana Smoking / Q000453:epidemiology* / Q000517:prevention & control* / Q000523:psychology; D015397:Program Evaluation / Q000706:statistics & numerical data*; D012306:Risk
keywords: Cannabis/marijuana use; Prevention intervention; Randomized controlled trial; Risk behaviors; Risk groups; Unplugged