# Development and Comparability of Internalizing and Externalizing Symptom Spectra From Adolescence to Young Adulthood

## TL;DR

This study tracks how mental health symptoms in adolescents relate to similar issues in young adulthood, showing continuity in symptom patterns over time.

## Contribution

The study demonstrates that harmonized approaches can bridge measurement gaps in longitudinal psychopathology research.

## Key findings

- Adolescent emotional and peer problems predict internalizing symptoms in young adulthood.
- Conduct problems and hyperactivity in adolescence predict externalizing traits in adulthood.
- Substance use in adolescence is linked to hyperactivity and risky drinking but not peer problems.

## Abstract

This study examines the continuity and comparability of internalizing and externalizing symptom spectra from adolescence to young adulthood, addressing measurement challenges across developmental stages. Leveraging the Hierarchical Taxonomy of Psychopathology (HiTOP) framework, it explores whether symptom spectra in adolescence predict corresponding symptoms in young adulthood.

Data were drawn from JEPSY, a follow‐up of the national KiGGS cohort (N = 2172, age 18–26). Adolescent internalizing and externalizing symptoms were assessed via the Strengths and Difficulties Questionnaire (SDQ) and substance use items. Adult outcomes included the Patient Health Questionnaire (PHQ‐4), DSM‐5 Cross‐Cutting Symptom Measure (DSM‐5 CC), and Personality Inventory for DSM‐5 (PID‐5). Factor analyses assessed structural consistency, and robust regression examined associations between adolescent and adult symptom spectra over 7–10 years.

A four‐factor model best captured the SDQ structure. In young adulthood, three spectra emerged: internalizing symptoms, externalizing traits, and substance use. Adolescent emotional and peer problems predicted internalizing symptoms in adulthood. Conduct problems and hyperactivity predicted externalizing traits. Substance use was associated with hyperactivity, smoking, and risky drinking—but negatively with peer problems.

The findings support the continuity of broad psychopathological spectra and demonstrate that harmonized approaches can bridge measurement gaps and enhance longitudinal comparability.