We performed meta-analyses of GWASs of DSM-defined nicotine dependence (hereafter referred to as “DSM-NicDep”) across a total of 18 cohorts, 3 of which included samples of multiple ancestries, using a sample size-weighted meta-analysis implemented in METAL (Willer, Li, & Abecasis, 2010). We used nicotine-exposed controls where possible (see Supplemental Materials for more details on each cohort). The deCODE and Finnish Twin Cohort samples were entirely of EUR. For other cohorts, genetic ancestry similarity was inferred by comparing an individual’s genome to the genomes from global reference populations using statistical methods such as principal components analysis. Specifically, all Psychiatric Genomics Consortium cohorts included in this meta-analysis used the 1,000 Genomes Phase 3 as a reference panel for defining ancestries based on principal components, as did the Thai sample. There were 16 cohorts with samples that were most genetically similar to EUR global reference populations, 4 with samples that were most genetically similar to African ancestry (AFR) global reference populations, and 1 cohort whose participants were most genetically similar to East Asian ancestry (EAS) global reference populations (hereafter referred to as European,
