# Integration of former child and adolescent study participants into a national health online panel for a longitudinal study on young adult mental health

## TL;DR

This study shows how former child participants in a health survey were successfully re-contacted for a new online mental health study as young adults.

## Contribution

The study introduces a method for re-engaging former participants in longitudinal research using a modern online panel.

## Key findings

- 37.9% of invited former participants registered for the new online panel.
- Females and individuals with higher occupational or educational status were more likely to register and participate.
- Weighting adjustments reduced selection bias but increased statistical variance.

## Abstract

Longitudinal studies are essential for understanding health trajectories and determinants over time. Successfully re-engaging and monitoring participants at key stages such as the transition from adolescence to adulthood is crucial. This stage of life is characterized by many changes and challenges and is considered critical for the manifestation of mental health problems. This study addresses challenges of contacting, re-activation and comparability of individuals in transition to adulthood with the initial population-based sample last contacted up to 9 years ago.

In 2024, former participants of the “German Health Interview and Examination Survey for Children and Adolescents” (KiGGS) aged 16–25 years were invited to register in the new online panel infrastructure “Health in Germany” and participate in the “Study on Mental Health in Emerging Adulthood” (JEPSY) via a push-to-online panel approach. Logistic regression models identified predictors of registration and study participation. Weighting adjustments were applied to analyse and correct for selective participation. To assess potential selection bias, life satisfaction of JEPSY participants was benchmarked against a representative sample.

Among 11,737 invitees, 4,451 (37.9%) registered, and among these, 3,063 (68.8%) completed the JEPSY survey. For participants aged 11 + years, higher probabilities for registration and participation were evident for females (OR = 2.61 [95% CI: 2.37–2.88]); OR = 2.85, [2.56–3.18]), individuals with higher occupational (OR = 1.08, [1.04–1.13]; OR = 1.06, [1.01–1.11]) or educational status (OR = 1.13, [1.08–1.17]; OR = 1.13, [1.08–1.17]). Individuals with higher emotional problems were less likely to register (OR = 0.98, [0.97–0.99]) and participate (OR = 0.98, [0.97–0.99]). Weighting adjustments reduced biases but increased statistical variance. Benchmarking life satisfaction revealed no significant differences between JEPSY participants and their representative counterparts.

This study demonstrated the feasibility of re-activating former participants and integrating them into a modern online panel. While re-activation was successful for a substantial proportion of invitees, specific challenges (e.g., selective re-participation) remain. The findings provide insights for refining re-contact and retention strategies to improve representativeness and quality of longitudinal mental health research, ultimately enabling more accurate monitoring of health trajectories and their determinants over time.

The online version contains supplementary material available at 10.1186/s12874-025-02613-2.