Research is increasingly demonstrating genetic influences on many aspects of human functioning. However, because genetic factors are unlikely to account for all variations in functioning, it is essential to analyze the interplay of genetic, environmental, and methodological effects on specific measures of functioning. Using CBCL ratings of 984 8- to 12-year-old twins participating in the Missouri Twin Study, Hudziak et al. (2000) found that genetic factors accounted for 60 to 68% of the variance in Attention Problems; 70 to 77% of the variance in Aggressive Behavior; and 61 to 65% of the variance in Anxious/Depressed syndrome scores.
There were thus large genetic effects on these syndromes. However, there were also moderate environmental effects, ranging from 23% of the variance in the Aggressive Behavior syndrome scores for boys to 40% of the variance in the Attention Problems syndrome scores for girls. In addition, Hudziak et al. found negligible rater bias effects on the CBCL syndrome scores. The lack of rater bias effects on the CBCL contrasted with findings for interviews and questionnaires using DSM criteria. The authors concluded that the intermingling of items tapping different syndromes on the CBCL helped to prevent rater biases that arise when symptoms are grouped together according to types of disorders.
Reference: Hudziak, J.J., Rudiger, L.P., Neale, M.C., Heath, A.C., & Todd, R.P. (2000). A twin study of inattentive, aggressive, and anxious/depressed behaviors. Journal of the American Academy of Child & Adolescent Psychiatry, 39, 469-476.