DNA was genotyped using the Illumina Addiction biology SNP array using the Illumina GoldenGate platform (Hodgkinson et al., 2008 (link)). GABRA2 SNP rs279858 (exon 5, K132K) was examined given prior work demonstrating associations between the minor allele and problem behavior and maladaptive personality (Trucco et al., 2014 (link); Villafuerte et al., 2013 (link)). All MLS participants (n=1139) were also genotyped for 150 ancestry informative markers (Hodgkinson et al., 2008 (link)), and ethnic factor scores were calculated using principal component analysis in SAS 9.3 as in prior work (Glaser et al., 2014 (link)). The four scores explaining the highest variance (~96%) were examined to control for population stratification.