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 the subject-specific deviation from the mean age slope; εti is the residual for subject i at assessment t. Random effects u0 and u1i were specified orthogonal. The term of interest, u1i, may more intuitively be described as the subject-specific alcohol consumption age trajectory. As subject-level parameters are not directly estimated by the mixed model, they were calculated as BLUPs in a post-estimation step (Pinheiro & Bates, 2000). See Supplementary Material 1 for further phenotypic modeling details.
