There was also a significant four-way interaction between the single-item CDP age of onset with medication group, genotype, and week (t = 2.33, p = 0.022). Among L′ homozygotes, there was a significant three-way interaction of age of onset, medication group, and week (t = 3.42, p = 0.003). Among S′ carriers, this interaction effect was not significant (t = 0.42, p = 0.68). Figure 2 looks very similar to Figure 1 from Kranzler et al. (2011), which also showed an interaction effect using the age of onset of alcoholism based on the SCID diagnosis of alcohol dependence rather than the single item from the CDP. All the parameter estimates for the single-item CDP age of onset were within the standard errors of the parameter estimates found by Kranzler et al. (2011) using the SCID-derived age of onset.
