We also note three measurement related issues. First, method invariance could account for some portion of the associations described in our findings, as both externalizing behavior and peer group antisocial behavior were derived from self-report. Thus, adolescents’ perceptions of the antisocial behaviors of their peers could bias their assessments of their own behaviors, and vice versa, whereas an objective measure of one or the other would remove any such dependencies in the data. However, these findings are consistent with prior examinations of the same sample which evidenced similar patterns of association between child-reported peer group antisocial behavior and teachers’ ratings of externalizing behavior (Laird et al., 1999; Lansford et al., 2003), as well as those from two other studies examining latent gene-environment interaction in relation to externalizing problems, both of which used peer-reported measures of peer deviance (Brendgen et al., 2008; van Lier et al., 2007). A second issue of measurement is related to the fact that externalizing behavior was measured via 30 items in each of the first six assessment periods, but only 28 items thereafter. Although the variance
