The study design, methods and procedures used in the IAS have been described previously [12, 13]. Briefly, in four waves, the records of approximately 11,700 adoptees in the state of Iowa were reviewed and their families solicited to provide 475 adoptees with a biological family history of substance use or ASPD and 475 adoptees without a family history of behavioral illness. Over the past 30 years, these adoptees and their environments have systematically assessed using a variety of standardized instrument and semi-structured interviews. In the last two waves of the study (1999–2004 and 2004-current), each of the subjects was interviewed using the Semi-Structured Assessment for the Genetics of Alcoholism, Version II (SSAGA-II) [14]. Using a clinical data from these interviews, symptom counts for MDD (maximum score of 9), ASPD (maximum score of 7), and substance use (alcohol, nicotine and marijuana, maximum score of 7) were derived using criteria from DSM-IV [15] as per our previous methods [12, 16].
