ran linear regression for AUDIT–P in UKB–EUR2 as a validation dataset using PRSEUR, PRSAFR and PRSLA as independent variables. The corresponding regression coefficients were used as weights in the test dataset (UKB–EUR1) to calculate the final PRS: PRSfinal = ωEUR × PRSEUR + ωAFR × PRSAFR + ωLA × PRSLA. We used linear regression to test the association between AUDIT–P and PRSfinal after standardization, correcting for age, sex and the first ten PCs. We also ran a null model of association between AUDIT–P and covariates only, to calculate the variance explained (R2) by PRSfinal. For comparison, we also calculated PRS in UKB–EUR1 using only the AUD summary data in EUR, then calculated the variance explained by PRSsingle. The improved PRS association was measured as the difference of the variance explained (ΔR2).
