BACKGROUND Epidemiological samples provide opportunity to understand the development of mental health trajectories to better understand whether such epidemiological data can help to plan and modify service delivery for youth mental health. Variation between countries is not well understood and thus applying evidence from other countries to national strategies limits support service policy and planning. We therefore examine developmental patterns of youth mental health across different countries using the Growing Up in Ireland (GUI) Cohorts, with comparison to existing UK longitudinal cohort data (Millennium Cohort Study, MCS; Growing up in Scotland, GUS).

METHODS Youth mental health problems within each cohort across development (5-17/18 years) were assessed using parent reported Strengths and Difficulties Questionnaire (SDQ) scores. Using latent growth curve analyses, we examined trajectories of emotional, conduct, and hyperactivity problems for boys and girls, separately for each cohort.

RESULTS Across cohorts, we observed similar developmental patterns for emotional, conduct, and hyperactivity problems. However, the GUI emotional problems in Ireland emerged earlier than in the UK. By adolescence, GUI emotional scores were similar to the UK, suggesting that the differences in emotional problems between the ROI and UK had narrowed by adolescence. Covariates also had different associations with youth mental health trajectories across cohorts.

CONCLUSIONS Utilizing multiple nationally representative cohort longitudinal datasets can help inform clinically meaningful conclusions and potential recommendations on population level multi-tiered service needs and development in the area of child and adolescent mental health support and future provision.