The basic structure of the two-part model tested in middle school is depicted in Figure 1, illustrating prediction to intercept and slope of both use and volume of use from Grade 6 predictors. In addition, the change scores for each predictor between Grades 6 and 8 (i.e., Grade 8 score minus Grade 6 score) were modeled to predict to the slopes. This allowed for a test of effects of changes in predictors on the slope factors while controlling for the initial predictor values. Paths from all Grade 6 predictors and the alcohol intercepts to each change score were included, and their residual influences were allowed to covary.
