Exploring ADHD Symptoms and Associated Impairment Across Development

Objective ADHD symptoms typically decline with age, but less is known about whether the presentation of specific ADHD symptoms differs across development. This study aimed to examine the frequency and associated impairment of specific ADHD symptoms in childhood, adolescence and young adulthood. Method A prospective, longitudinal cohort, the Avon Longitudinal Study of Parents and Children, was utilised (N=2327). ADHD symptoms and impairment were assessed using the Development and Well Being Assessment at ages 7, 15 and 25. Results Specific ADHD symptom frequencies and their associated impairment varied across development for the majority of symptoms, although easily distracted was one of the most commonly reported symptoms at each age, and difficulty sustaining attention was consistently associated with high levels of impairment. Conclusion These findings suggest differences in the presentations of ADHD symptoms across development: current understanding of how ADHD presents in childhood/adolescence may not be generalisable to young adulthood.

age 7 was recorded as one of the 3 least commonly reported symptoms in the whole sample, yet it was 7 th most commonly reported in those meeting diagnostic criteria for ADHD. The symptom 'avoids concentration tasks' at age 15 was one of 3 most commonly reported symptoms in the whole sample, but only the 10 th most commonly reported symptom in those meeting diagnostic criteria for ADHD and, the symptom 'difficulty calming down/relaxing' at age 25 was the most commonly reported symptom in the whole sample, but only 10 th most common in those meeting criteria for ADHD diagnosis.

Sex specific sensitivity analyses
Sensitivity analyses examined ADHD symptom frequencies and associated mean impairment score separately for males and females (Supplementary Tables 4 and 5 respectively). Results showed a similar pattern of results, although there were some differences in the most commonly ranked symptoms for boys and girls. There was also stronger evidence that some hyperactive-impulsive symptoms were more impairing at age 25 compared to age 7 for girls than boys (difficulty staying seated, blurting out answer and interrupts), and that some inattentive symptoms were more impairing at age 25 compared to age 7 for boys than girls (does not listen, does not finish task/job properly, difficulty sustaining attention).

Missing data sensitivity analyses
Sensitivity analyses were conducted (i) using 'complete case analyses' (i.e. N=2327 without IPW) and (ii) including anyone with any ADHD data (maximum N=8805). These approaches showed a a similar pattern of results to the primary (IPW) analyses (Supplementary Tables 6 and 7).

Supplementary Table 1
Comparison of the Descriptions of the DSM-5 ADHD Symptom Criteria With our Study and the DAWBA Questionnaire at Ages 7, 15 and 25 years DSM-5 Criteria (American Psychiatric Association, 2013) Symptom Often blurts out an answer before a question has been completed (e.g., completes people's sentences; cannot wait for turn in conversation).

Blurts out answers
Does s/he often blurt out an answer before s/he has heard the question properly?
Does s/he often blurt out an answer before s/he had heard the question properly?
Does s/he often blurt out an answer before s/he has heard the question properly or finish other people's questions for them?
HAI 7 Often has difficulty waiting his or her turn (e.g., while waiting in line). Often does not seem to listen when spoken to directly (e.g., mind seems elsewhere, even in the absence of any obvious distraction).
Does not listen Often does not follow through on instructions and fails to finish schoolwork, chores, or duties in the workplace (e.g., starts tasks but quickly loses focus and is easily side-tracked).
Does not finish a task/job properly Does s/he often not finish a job properly?
Does s/he often not finish a job properly?
Does s/he often not finish a job properly?
IA 5 Often has difficulty organizing tasks and activities (e.g., difficulty managing sequential tasks; difficulty keeping materials and belongings in order; messy, disorganized work; has poor time management; fails to meet deadlines).

Difficulty organising
Is it often hard for him/ her to get herself organised to do something?
Is it hard for him/her to get himself/herself organised to do something?
Is it often hard for him/her to get himself/herself organised to do something?
IA 6 Often avoids, dislikes, or is reluctant to engage in tasks that require sustained mental effort (e.g., schoolwork or homework; for older adolescents and adults, preparing reports, completing forms, reviewing lengthy papers). Have these problems put a burden on you or the family as a whole?

Avoids concentration tasks
Have these difficulties with activity or concentration put a burden on you or the family as a whole?

Supplementary
Means not reported where N<5. ADHD SYMPTOMS AND ASSOCIATED IMPAIRMENT Note. Residual variances fixed to 1 for models A and B. CFI = comparative fit index, RMSEA = root-mean-square error of approximation, SRMR = standardized root mean squared residual.