title: Effectiveness of Motivational Incentives for Adolescent Marijuana Users in a School-Based Intervention.
abstract: OBJECTIVE
  This study examined whether adolescents receiving Motivational Interviewing (MI) intervention have different outcomes compared to those receiving Motivational Incentives (Motivational Interviewing combined with Contingency Management; MI+CM).
  
  
  METHODS
  A total of 136 adolescents (from a parent study of 220 adolescents) with problematic substance use were recruited from 8 high schools in Washington State, where they completed either 8-weeks of MI or MI+CM. Frequency of marijuana use was assessed at baseline, at the end-of-treatment, and at 16-week follow-up.
  
  
  RESULTS
  A balanced and matched sample was created using propensity scores, then analyzed using Hierarchical Linear Modeling (HLM). Multilevel regression analyses revealed that adolescents who received MI+CM exhibited a greater reduction in use across time (p<.05). Reductions at the end-of-treatment were greater for the MI+CM condition (Cohen's d=-.82) compared to MI alone (Cohen's d=-.33), but did not differ at 16-week follow-up. Adolescents receiving MI+CM showed significantly fewer negative consequences of marijuana use at the end-of-treatment (t1, 124=2.26, p<.05), higher use of coping strategies (t1, 124=3.01, p<.01), and increased likelihood to attend additional treatment for substance use (χ2 1, 124=4.12 p<.05), though hypothesized improvements in motivation and school attendance were not found. Use of coping strategies at the end-of-treatment had a significant indirect effect on the relationship between the intervention condition and marijuana use at the end-of-treatment (F3, 121=10.20, R2=.20, p<.01).
  
  
  CONCLUSIONS
  These results suggest that the inclusion of contingencies into adolescent marijuana treatment decreases the end-of-treatment frequency of marijuana use and related consequences while increasing the use of coping strategies and the pursuit of additional treatment.
authors.affiliation: Seattle Pacific University. Electronic address: davidste@spu.edu.
authors.forename: David G
authors.initials: DG
authors.lastname: Stewart
authors.affiliation: University of California, San Diego.
authors.forename: Benjamin I
authors.initials: BI
authors.lastname: Felleman
authors.affiliation: University of Vermont.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Arger
mesh_terms: D000293:Adolescent; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000523:psychology / Q000628:therapy*; D008385:Marijuana Smoking / Q000523:psychology*; D009042:Motivation; D062405:Motivational Interviewing; D012574:Schools; D016896:Treatment Outcome; D055815:Young Adult
keywords: Adolescent substance abuse; Contingency management; Marijuana; Motivational incentives; Motivational interviewing; Propensity scores; School-based intervention