Although functional impairment is required for a diagnosis in the DSM 5, the time frame and definition of functional impairment is ambiguous. We present a conceptual review clarifying the difference between functional impairment as a stable trait representing strength or disability in various domains, and functional impairment as secondary to emotional or behavior problems, which is a state sensitive to change with treatment intervention. Functional impairment as a measure of treatment outcome includes both change from baseline and status at the endpoint of treatment. When using a validated measure of function, functional improvement can be defined as the percentage of patients who achieve the Minimal Important Clinical Difference (MCID) and functional remission as the percentage of patients who normalize at treatment endpoint. True treatment remission should be defined as both symptomatic and functional remission.
Keywords: ADHD; attention deficits; endpoint treatment; functional impairment; hyperactivity; measurement; outcome; rating scales; remission.