In this study, we compared two additional alcoholic subtype categorization methods to the method employed by Kranzler et al. (2011). Specifically, we examined a cluster analytic classification (Babor et al. 2002) with one based on the age of onset of alcohol problems, which was determined using a single item. Based on the findings that the interaction of subtype by medication was significant only when conditioned on variation in the serotonin-transporter-linked promoter region (5-HTTLPR) (Kranzler et al. 2011), we included genotype as a variable in the comparisons involving treatment outcome. Because in that prior study, the effect was limited to individuals with the L′L′ genotype, we anticipated that any differences would be limited to that genotype group.
