60. Zahn-Waxler, C., Schmitz, S., Fulker, D. W., Robinson, J., & Emde, R. (1996). Behavior problems in 5-year-old monozygotic and dizygotic twins: Genetic and environmental influences, patterns of regulation and internalization of control. Development and Psychopathology, 8, 103-122.

Genetic and shared environmental influences on behavior problems of 5-year-old twins were assessed, based on mother, father and teacher reports. Genetic influence for Externalizing Problems was consistently identified across informants. Effects of shared environment were present, but less consistently. Both genetic and environmental influences on Internalizing Problems were also identified, again with less consistency. Correlations between observed patterns of regulation at ages 3, 4, and 5, and behavior problems at age 5 were often significant, but low in magnitude and restricted to teachers' reports.