In the current study, our twin sample was assessed at two ages (12 and 17 years) that basically flank adolescence. In contrast, our previous study on the etiology of behavioral disinhibition (Young et al., 2000), was conducted with twins who spanned the adolescent age range (ages 12–18 years), with an average age of 14.2 years. Considering the developmental nature of the behavioral problems under study, we might expect results from our current Wave 1 analyses to align more closely with our previous findings. Indeed the etiological structure of behavioral disinhibition at Wave 1 is quite similar to that in our previous report. It is important to note that in our previous article, we reported a parsimonious model for behavioral disinhibition in which nonsignificant parameters were dropped from the model. If the same procedure were carried out on the current Wave 1 model (i.e., dropping the nonsignificant influences of shared environment, C), the heritability of behavioral disinhibition would be consistently quite high. Interestingly, our Wave 2 findings are more comparable to our previous study in terms of the pattern of factor loadings, in that the contributions of the individual components of behavioral disinhibition are more balanced.
