Young men were said to have an externalizing disorder if they had lifetime ADHD, ODD, CD, AAB, or earlier onset alcohol abuse or dependence, drug abuse or dependence, or nicotine dependence. The inclusion of nicotine dependence reflected its emergence as a strongly heritable indicator of externalizing in MTFS youths (McGue, Iacono, & Krueger, 2006), coupled with the fact that when included as part of the externalizing composite, the composite was genetically related to P300 amplitude (Hicks et al., 2007). The inclusion of substance abuse in this definition was intended to reduce the number of false negatives in the disorder-free group.
