Due to the relative paucity of research in this area, the scope of the literature review was expanded to include studies with some degree of racial or ethnic diversity. Some of these studies reported G–E results separately for each population included21,42,43, while others reflected the results of a combined sample44–49. These multi-population studies primarily included European Americans and African Americans, although some did include subjects of Latino/Hispanic or Asian descent. The search was also expanded to studies that examined both alcohol and other substance use phenotypes26,27,29–31,40. Therefore, the included studies either examined alcohol use discretely or as a part of a composite measure of substance use or risky behavior.
