Structure and trends of externalizing and internalizing psychiatric symptoms and gender differences among adolescents in the US from 1991 to 2018.

PURPOSE We aimed to estimate the structure of internalizing and externalizing symptoms and potential time dynamics in their association. This is understudied among adolescents, despite increasing internalizing and decreasing externalizing symptoms in recent years. METHODS We analyzed data from US Monitoring the Future cross-sectional surveys (1991-2018) representative of school-attending adolescents (N = 304,542). Exploratory factor analysis using maximum likelihood estimation method and promax rotation resulted in a two-factor solution (factor correlation r = 0.24) that differentiated eight internalizing and seven conduct-related externalizing symptoms. Time-varying effect modification linear regression models estimated the association between standardized internalizing and externalizing symptoms factor scores over time overall and by gender. RESULTS In 2012, trends in average factor scores diverged for internalizing and externalizing factors. The average standardized internalizing factor score increased from - 0.03 in 2012 to 0.06 in 2013 and the average externalizing factor score decreased from - 0.06 in 2011 to - 0.13 in 2012. We found that for every one-unit increase in standardized internalizing factor score, standardized externalizing factor score increased by 0.224 units in 2010 (95% CI: 0.215, 0.233); the magnitude of this increase was 22.3% lower in 2018 (i.e., 0.174 units; 95% CI: 0.160, 0.188). Decoupling of internalizing and externalizing symptoms began earlier among boys (~ 1995) than among girls (~ 2010). CONCLUSION The decoupling of internalizing and externalizing symptoms among adolescents suggests that changes in the prevalence of shared risk factors for adolescent psychiatric symptoms affect these dimensions in opposing directions, raising the importance of considering symptoms and their risk factors together in prevention and intervention efforts.