We first estimated an unconditional LGCM. Time points were fixed incrementally to reflect the annual assessment schedule (i.e., age 12 fixed at 0, age 13 fixed at 1, age 14 fixed at 2, and age 15 fixed at 3). We expected that the intercept and slope variance and slope mean parameters would be significant, indicating variability around age 12 alcohol use and change over time, as well as a steady increase in alcohol use propensity between 12 and 15 years. We then tested the fit of the model conditioned on race, and age 11 household poverty, conduct problems, impulsivity, and menarche. Risky sex at age 16 was regressed on the growth model, and the putative interaction between race and the slope of alcohol use predicting risky sex at age 16 was tested using a series of nested multiple group latent growth curve models (cf. Muthén and Curran 1997). The nested model constrained a single parameter (e.g., path coefficient) to be equal for African American and European American girls. We used a χ2 difference test to compare the nested model with
