Substance use development is confounded with environmental change during adolescence. As youths age it is arguable that their home environment changes to accommodate an increased expectation of autonomy, and increased needs for independence. In the United States, for example, one can legally drive an automobile at age 16, legally purchase tobacco products at 18, and legally purchase alcohol at 21, all of which are within the time interval under investigation in this study. While a caregiver may restrict automobile or substance use, it is clear that developmental maturation can be confounded with dramatic environmental shifts in substance availability and social norms surrounding use. In fact, this observation can easily explain the current findings. Adolescents at age 14 or 17 may have a genotype that increases their CPD but are unable to satisfy that risk because cigarettes are not readily available to them, thus the SNP score’s effect is moderated not by developmental neurological or biological maturation, but by a developmentally-confounded environment (i.e., development serves as a proxy for environmental change). Add to this the extra complication that individuals with riskier
