Looking beyond the individual: The relative importance of neighbourhood socioeconomic status and the development of internalising symptoms across adolescence

• Six waves of longitudinal data from 1,556 Australian adolescents aged 13 to 16 yeas were analysed. • Four distinct internalising symptoms trajectories were identified: Low stable (49% of adolescents), Increasing (30.6%), Decreasing (10%), and High Increasing (10.2%). • Neighbourhood socioeconomic disadvantage was associated with membership in a High Increasing internalising symptom course, relative to the Low Stable class, controlling for covariates (gender, age, externalizing symptoms) Mental disorders have considerable impact on individual and societal well-being, with peak onset during adolescence. This study explored the relationship between neighbourhood socioeconomic status and internalising symptom progression during adolescence. Longitudinal data from 1,556 adolescents was taken from the control group of a cluster-randomised controlled trial of school-based prevention program for mental health and substance use. Measures assessed internalising symptoms (SDQ) across six time points from 13 to 16 years and the Index of Relative Socioeconomic Advantage and Disadvantage (IRSAD) was used to measure participants’ neighbourhood socioeconomic status (SES) at baseline. Latent class growth analysis was used to estimate different internalising symptom trajectories among adolescents. Multinomial logistic regression explored the relationship between SES and internalising trajectory class, controlling for covariates. Four distinct trajectories of internalising symptoms were identified: Low stable (49% of adolescents), Increasing (30.6%), Decreasing (10%), and High Increasing (10.2%). Lower neighbourhood SES was associated with an increased likelihood of belonging to the High Increasing class relative to the Low Stable group. Additionally, female gender and baseline externalising symptoms were associated with an increased likelihood of belonging to all three elevated symptom trajectories compared to the low stable class, controlling for SES and other covariates. The findings provide novel insight into the negative relationship between neighbourhood disadvantage on individual mental health trajectories, above and beyond individual factors, during adolescence. The findings have significant implications for social and economic policies.