Strong environmental influences could still segregate individuals into distinct trajectories. However, shared environmental influences are mostly weak,41,42 and unique environmental influences, though sometimes strong, are stochastic and therefore often intractable to exact study. Furthermore, the individual differences most strongly correlated with alcohol use—such as externalizing psychopathology, internalizing psychopathology, and traits related to behavioral disinhibition and neuroticism—are themselves continuously distributed and shaped by myriad genetic and environmental influences. Theoretical models may yet explain how small forces aggregate to produce discrete alcohol use trajectories (e.g., dynamic systems theory43), and sophisticated analytic techniques may yet identify them (e.g., free-curve slope intercept models44). However, using the most common methods in contemporary alcohol trajectory research, the current study does not provide evidence supporting the validity of distinct trajectory groups.
