Taken together, these findings suggest greater incidence risk and lifetime prevalence of substance abuse during adolescence than has been estimated from adult samples.14–17 Such differences are likely to reflect the inclusion of older-onset cases in investigations of adults and increases in retrospective memory biases in these samples. It also remains possible that younger cohorts are more likely to use specific substances or to use them at an earlier age. In this regard, the conditional analyses demonstrate that the risk of abuse among users is particularly high among the youngest adolescents. The conditional rate for abuse with or without dependence among the youngest drug users (13–14 years old) is 10-fold the unconditional rate (35.4% vs 3.4%). By contrast, the conditional rate of abuse with or without dependence among the oldest adolescents is just more than twice the unconditional rate (38.6% vs 16.4%). Although high conditional rates in younger adolescents may be partly attributable to the low unconditional prevalences, they nonetheless pinpoint early adolescence as a period of heightened risk for substance use and abuse.29,30 The elevated rate and risk of substance
