or dependence of cocaine, stimulants, sedatives, opioids, or marijuana. Because AD is so frequently comorbid with other types of substance dependence, cases meeting diagnostic criteria for other types of dependence were not excluded: 49.9% (N=226) of cases were marijuana dependent; 40.7% (N=188) were cocaine dependent; 30.6% (N=140) were dependent on stimulants; 20.6% (N=87) were dependent on sedatives; and 18.8% (N=85) were opioid dependent. Because COGA probands were recruited in part from treatment centers, they likely represent relatively severe cases of alcohol dependence. In addition, the cases used in this study, who also meet Criterion A for a major depressive episode, endorsed more AD symptoms than cases without a history of depression (see Discussion). Thus, the cases included in this analysis likely represent an extreme phenotype.
