Analyses were performed using Haploview (Barrett et al., 2005) and SAS software (version 9.2; SAS Institute, Cary, NC). Inter-correlations between the 12 CNR1 tSNPs were analyzed with pair-wise linkage disequilibrium (LD) statistics within Haploview. Because only a minority of the sample had heavy marijuana misuse, we grouped patients with marijuana abuse and patients with marijuana dependence together (N=52) for statistical analyses. Furthermore, since there were no significant group differences in sociodemographics, illness characteristics, MRI brain volumes or CNR1 tSNP allele frequencies between patients without prior marijuana exposure and patients whose marijuana use had not meet DSM marijuana abuse or dependence (data not shown; available upon request), these patients were grouped together (N=183) for comparison against patients with marijuana abuse or dependence. Group differences on categorical variables were tested using χ2-test and continuous variables independent group T-test or ANCOVA.
