The Michigan State University Twin Registry (MSUTR) includes several independent twin projects (Burt & Klump, 2013a). The 500 twin pairs (50.2% monozygotic; MZ) included in the current study were assessed as part of the Twin Study of Behavioral and Emotional Development in Children within the MSUTR. Participating twins did not differ from non-participating twins in their average levels of conduct problems, emotional symptoms or hyperactivity (Cohen’s d=−0.05, 0.01 and −0.08, respectively). Moreover, participating families endorsed ethnic group memberships at rates comparable with area inhabitants (e.g. Caucasian: 86.4% and 85.5%, African-American: 5.4% and 6.3% for the participating families and the local census, respectively). More detailed information regarding the design, recruitment procedures, representativeness and participation rates have been provided elsewhere (Burt & Klump, 2013a).
