How much impairment is required for ADHD? No evidence of a discrete threshold

Trine Wigh Arildskov*, Edmund J.S. Sonuga-Barke, Per Hove Thomsen, Anne Virring, Søren D. Østergaard

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)


Background: A diagnosis of attention-deficit/hyperactivity disorder (ADHD) requires the presence of impairment alongside symptoms above a specific frequency and severity threshold. However, the question of whether that symptom threshold represents anything more than an arbitrary cutoff on a continuum of impairment requires further empirical study. Therefore, we present the first study investigating if the relationship between ADHD symptom severity and functional impairment is nonlinear in a way that suggests a discrete, nonarbitrary symptom level threshold associated with a marked step increase in impairment. Methods: Parent reports on the ADHD-Rating Scale (ADHD-RS-IV), the Weiss Functional Impairment Rating Scale (WFIRS-P), and the Strengths and Difficulties Questionnaire were collected in a general population sample of 1st, 2nd, and 3rd graders (N = 1,914–2,044). Results: Piecewise linear regression analyses and nonlinear regression modeling both demonstrated that the relationship between symptom severity (ADHD-RS-IV total score) and impairment (WFIRS-P mean score) was characterized by a gradual linear increase in impairment with higher symptom severity and no apparent step increase or changing rate of increase in impairment at a certain high ADHD-RS-IV total score level. Controlling for socioeconomic status, sex, and co-occurring conduct and emotional symptoms did not alter these results, though comorbid symptoms had a significant effect on impairment. Conclusions: There was no clear evidence for a discrete, nonarbitrary symptom severity threshold with regard to impairment. The results highlight the continued need to consider both symptoms and impairment in the diagnosis of ADHD.

Original languageEnglish
JournalJournal of Child Psychology and Psychiatry and Allied Disciplines
Issue number2
Early online date27 May 2021
Publication statusE-pub ahead of print - 27 May 2021


  • Attention-deficit/hyperactivity disorder
  • continuity
  • diagnosis
  • schoolchildren
  • symptomatology


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