This study modeled trajectories of alcohol and marijuana use from ages 15 to 20 among 1,095 male serious juvenile offenders and predicted trajectories from risk and protective factors before and after controlling for time spent in a supervised setting.
Consistent with findings from the general population, the study found that alcohol and marijuana use had (on average) initially occurred by age 15, and there was significant growth in these trajectories between ages 15 and 20. After considering total time spent in a supervised facility, estimates for rate of change in substance use increased. Consistent with previous research, the current study indicates that omitting the effects of supervised time can produce distorted estimates of substance-use frequency and underestimate the increases in substance use over time among serious juvenile offenders. The study also found that substance use was less likely to increase with age for those offenders who spent greater mounts of time in a supervised setting. This suggests that supervised time may suppress the trajectories of substance use for adolescent offenders. The variation in substance use in relation to amount of supervised time suggests a simple suppressing effect of supervised time, with more time spent in a restricted setting equal to less opportunity for an increase in substance use; however, for marijuana, the magnitude of increase in marijuana use did not differ between youth with no supervised time and youth with low levels of supervised time. The possibility that the data reflect both incapacitation and selection effects suggest that caution is warranted in interpreting the effects of supervised time on substance-use trajectories. The two self-reported substance-use outcomes were frequency of past 6-month alcohol use and frequency of past 6-month marijuana use. At each wave of data collection, participants self-reported their frequency of alcohol and marijuana use. 3 tables, 1 figure, and 58 references