In modeling the developmental trajectories, we tested several specifications of age-based longitudinal change including linear and quadratic functions, as well as a series of piecewise plateau models specifying linear change until a given age and flat thereafter (Bollen & Curran, 2005). Model comparisons using likelihood ratio tests for nested models, and BIC/AIC for non-nested quadratic and piecewise models (Burnham & Anderson, 2004), indicated that a piecewise model with alcohol consumption stabilizing at approximately age 28 best fit the data. Thus, the preferred model used to generate our trajectory slope outcome can be written as: Yti=β00+β10ati+u0i+u1iati+εti where i and t are subject and assessment occasions, respectively; y is the alcohol consumption for subject i at assessment t; β00 is the overall sample intercept; β10 is the mean age slope coefficient for age specification a which is coded 0 for the earliest age observed in the sample, 1 for second earliest age, and so forth, until reaching the plateau age (~28), after which its value remains constant for subsequent ages; u0i is the subject-specific deviation from that overall sample intercept; u1i is
