MPlus version 5.0 (Muthen & Muthen, 1998–2007) was used to conduct all statistical analyses. MPlus uses maximum likelihood estimation, enabling us to retain participants for whom only incomplete data are available. We first constructed latent factors for overall externalizing behavior, aggression, and delinquency, using data from multiple sources across multiple points in time, as described above. We then regressed each of these outcome phenotypes onto genotype, physical harm, and a product term reflecting interaction between these two variables. Males carrying a high-activity allele are coded as “0” and those carrying a low-activity allele are coded as “1”.
