We estimated unconditional linear growth models for each substance to assess the trajectory of substance use over the three time points. Results indicated a linear, although non-significant, increase in alcohol, tobacco, marijuana, other drugs, and use of any drugs over the three time points. Variance components were not significant in any of the unconditional models but follow-up chi-square analyses indicated significant differences on substance use in the intervention and comparison group at baseline and thus a variance component was included at the intercept to account for this variability.
