We utilized a latent change score approach using latent curve models. The previous study (White et al., 2007) showed that overall substance use decreased between baseline and the 4-month follow-up assessment and increased between the 4-month and 15-month follow-up assessments. Instead of analyzing this change pattern using typical nonlinear latent curve models, we examined latent changes between baseline and the first follow-up at 4 months (i.e., latent change variable, initial change [IC] in Figure 2), and between 4 months and 15 months post intervention (i.e., latent change variable, subsequent change [SC] in Figure 2).7 We specified the outcome levels at 15 months post intervention as the intercept level (i.e., latent variable, level in Figure 2) because participants in the present study were randomly assigned to a treatment condition and there were no group differences between the BMI and WF groups at baseline. Thus, we focused on the long-term outcome levels rather than baseline levels. This intercept selection approach is equivalent to centering a time metric variable at 15 months in latent curve models (see also the Appendix). All latent variable
