Relationships between alcohol milestones and continuously assessed executive function (EF) development were assessed with linear mixed effects models (lme4 R package; Bates, Mächler, Bolker, & Walker, 2015). Time-in-study was person-mean-centered and used to model linear and quadratic within-person trajectories of EF. Main effects of alcohol milestones (Supplemental Methods) and interactions with time-in-study were explored with respect to each EF dependent variable. Random slopes allowed for varying rates of (linear) change across individuals. Statistically significant omnibus tests for the overall interaction effects were followed by post hoc pairwise comparison tests. The same analytic process was repeated for PGS, with PGS of drinks per week and problematic alcohol use replacing the ‘milestone’ variable (Supplemental Methods).
