Overall, 14 of the 16 studies reviewed reported at least one significant GxE, whereas 11 studies reported one or more non-significant GxE (Table 2), and there were no clear patterns of gender differences in GxE (Table 1). Limited evidence for GxE in adoption studies may be due in part to the lower power of these specific studies to address GxE questions of this nature. Measurement of environmental risk was limited in the Swedish adoption studies, and the Iowa study was restricted by its small sample size. Additionally, the large number of non-significant findings and high probability of type I error suggest that studies of aggregate genetic influences may currently overstate the true effect size of alcohol-related GxE.
