This investigation sought to determine the structure of the comorbidity among four adolescent phenotypes indexing externalizing behaviors: hyperactivity/impulsivity, inattention, conduct problems, and alcohol problems. Specifically, we sought to examine measured familial/environmental risk factors and their associations with externalizing behavior and alcohol problems and, once taking those measured risks into account, to determine what proportion of the variance and covariance among these phenotypes was due to biological risk, environmental risk, or both.
