Previously there has been little research into the predictors and broader clinical meaningfulness of ADHD symptom developmental subtypes. Therefore, the authors investigated whether symptom trajectories associated with persistently high levels of ADHD symptoms from early life would tend to be associated with a broader range of risk factors for ADHD in later life.
Families from the UK who participated in the Millennium Cohort Study were sampled using a stratified sampling procedure. The study utilised data from children who were aged 9 months, 3, 5, 7, 11 and 14 years during the data collection sweeps. ADHD symptoms were measured at ages 3, 5, 7, 11 and 14 years using the hyperactivity/inattention subscale of the parent-reported Strengths and Difficulties Questionnaire (Goodman, 1997). The predictors of developmental trajectories, based on information gathered from the caregiver when the child was 9 months, included early child temperament, low birth weight, maternal educational level and prematurity. The caregiver was also interviewed when the child was aged 3 years to assess conduct problems, early child cognitive ability, emotional problems and peer problems.
In total, 11,315 participants were involved in the current study and were placed into symptom classes based on their ADHD symptom severity. A ‘pre-school onset persistent class’ of ADHD symptoms (6.4% of participants) showed a trajectory that was characterised by consistently high scores from age 3 years and had clinically significant scores for the entire study developmental period. The ‘pre-school onset partially remitting class’ (14.1%) showed scores that began in the borderline range but declined into the non-clinical range by around age 7 years. Additionally, a ‘subclinical remitting class’ (12.8%) showed initially elevated but subclinical scores at age 3 years that declined over development. The participants who were in the ‘pre-school onset partially remitting class’ and ‘subclinical remitting class’ were more likely to be female and had lower levels of conduct problems than those in the ‘pre-school onset persistent class’.
Furthermore, the ‘developmentally increasing class’ (7.6%) showed initially moderate or subclinical symptom levels that increased over development to reach borderline levels by age 11 years and clinically significant levels by age 14 years. The ‘developmentally increasing class’ were more likely to be female, have lower levels of conduct problems and higher school readiness scores compared with those in the ‘pre-school onset persistent class’. A ‘mildly affected class’ (24.1%) presented with slightly elevated but subclinical symptom levels that remained constant over their development. Finally, an ‘unaffected class’ (34.9%) showed consistently low levels of symptoms over development. Compared with the ‘unaffected class’, the ‘developmentally increasing class’ were more likely to be males born prematurely, have higher levels of conduct and peer problems at age 3 years and their mothers were in lower educational attainment categories.
There were several limitations to this study. First, the measure of ADHD was well-validated; however, it could not distinguish between hyperactivity, impulsivity and inattention and could not provide diagnostic information. Second, there was no clearly defined cut-off to indicate clinically significant symptoms. Third, only parent-reported data were available for all data sweeps; however, symptoms could manifest differently across settings and in interactions with different informants (Murray et al, 2018). Fourth, the long-term effect could not be assessed into adulthood. Fifth, the effects of ADHD treatment interventions were not assessed. Finally, the missing data methods assumed missing at random, as other missing data methods could not be tested; also, the extent that data were not missing at random and parameter estimates could be biased.
The authors stated that it could be possible to make clinically meaningful distinctions between a small number of ADHD trajectory groups, including ‘pre-school onset persistent,’ ‘pre-school onset remitting’ groups and a ‘developmentally increasing group’.
Read more about ADHD symptom trajectories here
Goodman R. The strengths and difficulties questionnaire: a research note. J Child Psychol Psychiatr 1997; 38: 581-586.
Murray AL, Booth T, Ribeaud D, Eisner M. Disagreeing about development: an analysis of parent‐teacher agreement in ADHD symptom trajectories across the elementary school years. Int J Methods Psychiatr Res 2018; 27: e1723
Murray AL, Hall HA, Speyer LG, et al. Developmental trajectories of ADHD symptoms in a large population-representative longitudinal study. Psychol Med 2021; Epub ahead of print.