With this proposed paradigm in mind, though, we first look at the proximal antecedents of conduct disorders (and other similar externalizing problems), with a focus on parent behaviors, parent-child interactions, family discord, and peer relationships. To begin, a mother smoking while pregnant can influence an adolescent's later externalizing disorders. Hill, Lowers, Locke-Wellman, and Shen (2000) examined the effects of maternal smoking during pregnancy on later adolescent psychiatric disorders. Using a sample of 150 18-year-old adolescents (eight to 18 years old at the initial assessment), the researchers assessed for evidence of depression, anxiety, conduct disorder, and oppositional defiant disorder (in essence, a less extreme version of conduct disorder). After controlling for confounding variables, maternal smoking during pregnancy was associated with the presence of oppositional defiance disorder at 18 years of age.