Information about the two sets of family samples was provided previously (25). Briefly, 854 subjects from 319 AA families and 761 subjects from 313 EA families were recruited. Each family included a sibling pair where both siblings were affected (at a minimum) with cocaine and/or opioid dependence (CD and/or OD). Subjects were interviewed using a computer-assisted version of the Semi-structured Assessment for Drug Dependence and Alcoholism (SSADDA) instrument (26). Individuals with a primary diagnosis of a major psychotic illness (e.g., schizophrenia or schizoaffective disorder) were excluded as probands. Additional siblings and parents of affected sibling pairs (ASPs) were recruited when possible regardless of their affection status. Family subjects were classified as genetically AAs or EAs based on a Bayesian model-based clustering method using the short tandem repeat (STR) marker linkage set as previously described (27).
