A 4-Group design variable was created to detect the genetic and environmental risk for offspring smoking outcomes based on the father's and father's co-twin DSM-III-R ND status which was obtained as part of the father's 1992 interview. Group 1 was comprised of offspring whose fathers had a lifetime diagnosis of DSM-III-R ND regardless of co-twins ND status and zygosity (high-genetic, high-environment (HG-HE) risk group). These offspring are posited to be at high genetic risk because of their father's history of ND and at high environmental risk by virtue of being reared by a ND father. Group 2 was comprised of offspring whose fathers did not have ND but the fathers' MZ co-twins (i.e., the offspring's uncle) met ND criteria, (high-genetic, low-environment (HG-LE) risk group). Group 3 was comprised of offspring whose fathers did not have ND but their DZ co-twins (i.e., offspring's uncle), met ND criteria (medium- genetic, low-environment (MG-LE) risk group). Offspring in the HG-LE group (group 2) are posited to have been at high genetic risk because their fathers share 100% of their genes with their ND cotwin,
