Analyses of non-response indicated no evidence for differences in participation for fathers with and without a substance use disorder (alcoholism or drug dependence) and their offspring (Duncan et al. 2008; Scherrer et al. 2004). Descriptions of survey contents and response rates have been previously published (Duncan et al. 2008; Scherrer et al. 2004), and a brief description is presented here. Project 1 resulted in the following response rates: of the 1,464 targeted twin fathers, 1,213 (83%) participated in the study as did 862 participating mothers (67% of 1,282 eligible) and 1,270 offspring 12–25 years of age (85.4% of 1,487 eligible) participated in the 2001 survey. In Project 2, of eligible twin fathers, 725 (81% of the 895 eligible) were interviewed, 427 (72.8% of the 601 eligible) mothers were interviewed and 839 offspring aged 12–32 (88% of the 950 eligible) participated in the 2003–2004 interviews.
