title: Alcohol and marijuana use trajectories in a diverse longitudinal sample of adolescents: examining use patterns from age 11 to 17 years.
abstract: We tested race/ethnic differences in alcohol and marijuana (AM) trajectories (comprising an intercept term, reflecting overall probability of use, and a slope term, reflecting change in probability of use) during adolescence, whether AM use trajectories predicted high school outcomes, and whether outcomes differed by race/ethnicity after controlling for trajectory of AM use.
  
  
  
  This longitudinal study involved 6509 youth from 16 middle schools in Southern California surveyed from age 11.5 (2008) to age 17 (2015) years; all surveys assessed AM use, and the final survey also examined high school outcomes.
  
  
  
  Youth completed five surveys in middle school and two on-line surveys in high school.
  
  
  
  The sample was 50% male and 80% non-white.
  
  
  
  Intercept (at 2.75 years post-baseline) and slope of AM use were examined as outcomes for race/ethnic differences. AM use trajectories were examined as predictors of academic performance and unpreparedness, social functioning, mental and physical health and delinquency.
  
  
  
  We found differences in trajectories of use by race/ethnicity, with white youth reporting a higher overall intercept of alcohol use compared to all other groups (versus Asian P < 0.001, black P = 0.001, multi-ethnic P = 0.008). Overall, examination of trajectories of use showed that adolescents with a higher alcohol use intercept term reported greater academic unpreparedness (P < 0.001) and delinquency (P < 0.001) at wave 7 in high school. In addition, youth with a higher intercept for marijuana use reported greater academic unpreparedness (P < 0.001) and delinquency (P < 0.001), and poorer academic performance (P = 0.032) and mental health (P = 0.002) in high school. At wave 7, compared to white youth, Hispanic and multi-ethnic youth reported poorer academic performance (P < 0.001 and P = 0.034, respectively); Asian, black and Hispanic youth reported higher academic unpreparedness (P < 0.001, P = 0.019, and P = 0.001); and Asian youth and multi-ethnic youth reported poorer physical health (P = 0.012 and P = 0.018) controlling for AM use.
  
  
  
  Greater AM use was associated with worse functioning in high school for all youth. After controlling for AM use, non-white youth reported worse outcomes in high school for academics and health.
authors.affiliation: RAND Corporation, Santa Monica, CA, USA. damico@rand.org.
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: D'Amico
authors.affiliation: RAND Corporation, Santa Monica, CA, USA.
authors.forename: Joan S
authors.initials: JS
authors.lastname: Tucker
authors.affiliation: RAND Corporation, Santa Monica, CA, USA.
authors.forename: Jeremy N V
authors.initials: JN
authors.lastname: Miles
authors.affiliation: RAND Corporation, Santa Monica, CA, USA.
authors.forename: Brett A
authors.initials: BA
authors.lastname: Ewing
authors.affiliation: RAND Corporation, Arlington, VA, USA.
authors.forename: Regina A
authors.initials: RA
authors.lastname: Shih
authors.affiliation: RAND Corporation, Santa Monica, CA, USA.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Pedersen
mesh_terms: D000073978:Academic Performance / Q000208:ethnology / Q000706:statistics & numerical data; D000293:Adolescent; D017677:Age Distribution; D002140:California / Q000453:epidemiology; D002648:Child; D005260:Female; D006304:Health Status; D006801:Humans; D007398:Interpersonal Relations; D007604:Juvenile Delinquency / Q000208:ethnology / Q000706:statistics & numerical data; D017846:Longitudinal Ligaments; D008297:Male; D000074609:Marijuana Use / Q000453:epidemiology* / Q000208:ethnology; D008603:Mental Health; D044469:Racial Groups / Q000208:ethnology; D012959:Socioeconomic Factors; D000066608:Underage Drinking / Q000208:ethnology / Q000706:statistics & numerical data*
keywords: Adolescents; alcohol; marijuana; race/ethnicity; substance use; trajectories