There was a significant four-way interaction of cluster type, medication group, genotype, and week on this outcome measure (t = 2.38, p = 0.019). Examination of the interaction revealed a three-way interaction of cluster type, medication group, and week among L′ homozygotes (t = 2.48, p = 0.022), but not S′ carriers (t = 1.07, p = 0.29). Figure 1 shows that, among L′ homozygotes, Type B subjects drank less frequently when treated with placebo than sertraline, while Type A subjects drank less frequently when treated with sertraline than placebo. The effects in S′ carriers were not statistically significant.
