Disparities in Rates of Cigarette Use, Regular Heavy Episodic Drinking, and Marijuana Use Across Ages 14-32: An Application of the Time-Varying Effect Model

Introduction. Substance use among adolescents and young adults is a significant concern due to the potential for serious acute and long term negative health outcomes. Differences in prevalence of substance use by gender and race/ethnicity during these ages have been well documented, yet an examination of these disparities across two decades spanning critical developmental periods will shed light on how these differences fluctuate, thereby indicating key ages for interventions targeted to population subgroups.  In this study, we apply time-varying effect models (TVEM) to longitudinal panel data to flexibly model substance use prevalence over developmental, near-continuous time.

Method. We used data from all waves of the National Longitudinal Study of Adolescent Health, which provided data from ages 14-32 (N=37,219 person-times). TVEM was used to examine differences in prevalence of cigarette use, regular heavy episodic drinking (HED), and marijuana use and how these differences by gender and race changed as a smooth function of time. This technique allowed for a more nuanced examination of behavior change than more standard methods permit, and the examination of time-specific windows during which disparities emerged.

Results. Overall prevalence of cigarette use, regular HED, and marijuana use peaked at ages 28.5, 21.8, and 20.6 years, respectively. Prevalence of the three substances was higher for males than females overall, although these differences changed over time. Rates of substance use were similar for males and females early in adolescence, but significant differences emerged by the late teens when use was more common among males. With regard to race, prevalence of the three substances was highest for Whites compared to Hispanics or African Americans. The differences between Whites vs. Hispanics or African Americans increased considerably from age 16 to 20, particularly for cigarette use. Differences in cigarette use by race/ethnicity were found across age, but were largest at age 18 when the use of cigarettes peaks for Whites, with the peak prevalence for Hispanics and African Americans occurring much later (age 29.1).

Conclusions. These results suggest that substance use, particularly for certain subgroups, continues well past early adolescence with peaks of use as late as 29 years old in some populations. This research also demonstrates that differences between population subgroups fluctuate considerably between early adolescence and young adulthood, suggesting that intervention programs may be more critical at different ages depending on gender and race/ethnicity.  These findings display how TVEM can advance our understanding of the nuances of substance use across developmental time.