We derived trajectories from AUI scores using Mplus, Version 7,34 using a 10-point scaling of the AUI for ease of interpretation. An AUI score of 0 represents almost no alcohol use and a score of 10 represents the maximum use—the highest possible alcohol frequency (nearly every day), quantity (10+ drinks), and symptoms of abuse and dependence. Because the distribution of AUI scores changes substantially across age, AUI scores were bundled into discrete units (i.e., scores of 0–.49 were coded as “0,” 0.50–1.49 were coded as “1,” and so on) and treated as count outcomes.35 Bundling the AUI scores into discrete units creates a count variable and allows a Poisson regression approach, which can directly model the distribution of the skewed data as well as accommodate changes in these distributions across age by using a consistent yardstick (thresholds). This is preferable to treating the AUI scores as continuous because doing so involves making erroneous assumptions about the normality of AUI scores—assumptions that invariably produce multiple normally distributed classes to accommodate the skewed data.
