of the PRS to a model improves the fit of the model, thus indicating unique variance attributable to the PRS, over and above covariates. As peer use was restricted to recall at age 12–17, we did not test whether trajectory membership influenced future peer use. The Bonferroni-corrected significance threshold for the PRS analyses was set at 0.0019 (corrected for 27 tests: 3 class comparisons x 9 PRS thresholds), while the significance threshold was set at α < 0.05 for the remaining analyses. In addition, to overcome concerns that uncertainty in class membership might have influenced results, we reran analyses for the most predictive PRS threshold using the BCH approach in MPlus45. In this approach, the LCGA model is fitted to data and weights are assigned to likelihood of membership in each class while simultaneously examining between-class differences in PRS and accounting for the effect of covariates on class membership (see Supplemental Materials).
