Trajectories of mental health difficulties from childhood to adolescence: Evidence from Growing Up in Ireland

Introduction

Many mental health difficulties first emerge in adolescence, a critical period that can have lasting impacts on later-life outcomes. Poor mental health in early life is associated with poorer physical health, disruptions to education and employment, lower life satisfaction and poorer mental health outcomes in adulthood. Recent research in several countries, including Ireland, has documented significant increases in mental health difficulties among young people, particularly emotional problems, over time. In this study, we examine how mental health difficulties evolve between childhood and adolescence, focusing on two types of mental health difficulties: internalising problems (such as emotional or peer problems) and externalising problems (such as conduct problems or hyperactivity). 

Data and Methods

We use data from the ’98 and ’08 Cohorts of Growing Up in Ireland, the national longitudinal study of children and young people, to examine how internalising and externalising difficulties evolve from ages 9–17 ('98 Cohort) and 3–13 ('08 Cohort). Internalising and externalising difficulties are based on scores from the Strengths and Difficulties Questionnaire (SDQ), completed by the young person’s primary caregiver (usually their mother). Group-based trajectory modelling is used to identify internalising and externalising difficulties trajectories and to examine how these vary by gender and cohort. As the two GUI Cohorts were born ten years apart, and have comparable data at ages 9 and 13, a cross-cohort comparison of levels and change in internalising and externalising scores between 9 and 13 is also undertaken. 

Results

Most young people show low levels of mental health difficulties, but differences are observed by gender, age and across the two cohorts. In general, girls display higher rates of internalising difficulties, while boys display higher rates of externalising difficulties. Internalising problems include emotional problems (e.g., often unhappy, down-hearted or tearful) or peer problems (e.g., picked on or bullied by other children) while externalising problems include conduct problems (e.g., often has temper tantrums) or hyperactivity (e.g., constantly fidgeting or squirming). 

The results of the group-based trajectory modelling show how internalising and externalising difficulties evolve from ages 9–17 for the '98 Cohort and ages 3–13 for the '08 Cohort. For example, for the ’98 Cohort, the results for internalising difficulties show that about 23 per cent of girls display high or increasing levels of internalising difficulties between the ages of 9 and 17. There is more stability in internalising difficulty levels among boys, although 12 per cent display consistently high levels of internalising difficulties at ages 9, 13 and 17. 

For externalising difficulties, levels are stable for both boys and girls between the ages of 9 and 17 for the ’98 Cohort (although higher overall for boys). For the ’08 Cohort, levels of externalising difficulties decline between the ages of 3 and 13, although there is a group of boys (11 per cent) who display consistently high levels of externalising difficulties at all ages between 3 and 13. 

The timing of the survey waves means that we can compare 9- and 13-year-olds a decade apart. This shows that girls born in 2008 experience higher levels of internalising difficulties at a younger age than their counterparts born ten years earlier in 1998.

Conclusions

The findings align with recent research showing that internalising difficulties are becoming more prevalent among young people, especially girls. This could be due to several factors such as use of social media, educational stress and expectations, and — for the younger cohort — the impact of COVID-19, as their age 13 data were collected during the pandemic. Externalising symptoms improve for most children as they age, but some boys in particular remain at high risk. Further research examining the ‘08 cohort at age 17 will be important in confirming whether the emerging differences between the two cohorts are sustained through adolescence, or whether they reflect an earlier transition to a more stable set of trajectories. The findings highlight the need for greater mental health supports for young people, as well as their parents, families, and wider communities (e.g., schools, youth groups). Such supports include primary prevention (e.g., programmes to enable young people to develop the strategies and coping mechanisms to deal with mental health difficulties), as well as access to appropriate mental health diagnosis and treatment.