Are Alcohol Trajectories a Useful Way of Identifying At-Risk Youth? A Multiwave Longitudinal-Epidemiologic Study

Trajectory approaches are a popular way of identifying subgroups of children and adolescents at high risk for developing alcohol use problems. However, mounting evidence challenges the meaning and utility of these putatively discrete alcohol trajectories, which can be analytically derived even in the absence of real subgroups. This study tests the hypothesis that alcohol trajectories may not reflect discrete groups-that the development of alcohol use is continuous rather than categorical.

A multiwave longitudinal-epidemiologic twin study was conducted using 3,762 twins (1,808 male and 1,954 female) aged 11 to 29 years from the Minnesota Center for Twin and Family Research (MCTFR). The main outcome measures included various assessments of substance use, psychopathology, personality, and cognitive ability.

Although multiple trajectories are derived from growth mixture modeling techniques, these trajectories are arrayed in a tiered spectrum of severity, from lower levels of use to higher levels of use. Trajectories show perfect rank-order stability throughout development, monotonic increases in heritability, and perfect rank-order correlations with established correlates of alcohol use, including other substance use behaviors, psychiatric disorders, personality traits, intelligence, and achievement.

Alcohol trajectories may represent continuous gradations rather than qualitatively distinct subgroups. If so, early detection and interventions for youth based on trajectory subtyping will be less useful than continuous liability assessments. Furthermore, a continuous account of development counters the notion that individuals are predestined to follow one of a few categorically distinct pathways and promotes the opposite idea-that development is mutable, and its continuous terrain can be traversed in many directions.