In adoptive families, sibling pairs were biologically unrelated to each other, although one sibling might be the biological offspring of at least one of the adoptive parents. All adoptees were placed permanently in their adoptive home prior to 2 years (average placement age = 4.7 months; SD=3.4). Information is not available on the birth parents of the adoptees. Adoptive parents provided information on the country of birth and ethnicity of participating adolescents. In non-adoptive families, siblings were full, biological siblings. Subsequent to participation, two adolescents were judged ineligible, resulting in a total sample of 1232 adolescents, 613 mothers, and 551 fathers. A complete description of the SIBS recruitment process can be found in McGue et al. (2007)13.
