We created genome-wide polygenic scores for EXT with ~1 million SNPs, adjusted for LD with PRS-CS42 (Supplementary Information section 5), among subjects from two hold-out samples selected for their detailed phenotypes related to externalizing and substance use (Supplementary Information section 5): (1) the National Longitudinal Study of Adolescent to Adult Health (Add Health; N = 5,107), a U.S.-based study of adolescents recruited from secondary schools in the mid-1990s; (2) the Collaborative Study on the Genetics of Alcoholism (COGA; N = 7,594), a U.S.-based study on genetic contributions to alcohol use disorders.
