All analyses were performed on genotyped data. Association analyses were conducted in PLINK38 for SNPs in the region on chromosome 8 encompassing the α6 and β3 subunits of nicotinic receptors (42600000 kb to 42800000 kb). Logistic regression with DSM-5 cocaine use disorder as the dependent variable was performed. Covariates included were age at interview as a continuous variable, gender, study, maximum lifetime FTND score (0–10, based on the Fagerström Test of Nicotine Dependence) to control for smoking status, and DSM-5 alcohol use disorder. Study was coded using two dummy variables (yes/no for two of the three studies) in order to control for differences in ascertainment. Haploview was run using the genotypes of the study population to determine the number of independent linkage disequilibrium (LD) bins in the region using a threshold of r2 ≥ 0.8. The Bonferroni correction used in this study is p = 0.002 (0.05/22), as the number of LD bins in the region examined is 22. A conditional analysis was conducted including allele dosage for the top associated SNP as a covariate in the logistic model.
