Lastly, we fit a series of longitudinal growth models for a composite alcohol use index (AUI) in Add Health (see Supplementary Note 4.5 for complete results). The best fitting model represented a quadratic change in AUI over time (with sex differences in slope), a significant association between EXT PGS and base levels of AUI (βEXT = 0.12, SEEXT = 0.01, PEXT = 1.46 × 10–18), and a significant association between ALCP-specific PGS and change in the linear component of age for AUI (βALCP-specific*AGE = 0.07, SEALCP-specific*AGE = 0.02, PALCP-specific*AGE = 5.70 × 10–5). We found no evidence of sex-specific effects of either PGS in stratified models. Figure 4 provides a visual representation of the results from this best-fitting longitudinal model across levels of each PGS (±1.5 SD). Individuals higher on EXT PGS experience higher levels of AUI across time and sex, whereas those with higher levels of ALCP-specific experience increased growth in AUI. Supplemental Table 7 presents comparisons of estimates from longitudinal models using ALCP-total PGS to those in the main text.
