A second independent sample used for replication came from the Collaborative Study on the Genetics of Alcoholism (COGA), a large family-based study that recruited alcohol-dependent AA and EA probands from treatment facilities across seven sites in the United States [33, 34]. Probands and their families were invited to participate. Additional individuals and their families were recruited from the same communities. All participants were administered a version of the SSAGA [32, 35] which also queried about illicit drugs including opioids and cocaine.
