eTable 1. Grades of severity of intellectual disability (ID): definition, features, and frequency among persons with ID.

Severity of ID	IQ	ICD-10	Cognitive reference age	Features	Prevalence rates among people with ID
Learning disturbance	70–85	F81.9	>12 years	Learning disturbance that is not severe enough to be considered an intellectual disability
Mild	50–69	F70.x	9–12 years	Slow learning performance, often delayed speech development, cultural techniques can be learned, independent living is possible, occupational traning is possible	About 80%
Moderate	35–49	F71.x	6–9 years	Delayed language development, often with a reduced vocabulary, often delayed motor development, indepenent living may be possible with support as needed, work in a protected workplace or on a simple task is posible, cultural techniques can be learned with certain limitations	About 12%
Severe	20–34	F72.x	3–6 years	Marked impairment of language comprehension, has no active language or can only produce individual words, needs comprehensive support in the activities of daily life	About 7%
Very severe	<20	F73.x	0–3 years	Verbal communication impossible or nearly so, needs comprehensive support in self-care and in the activities of daily life, often incontinent, somatic comorbidities (e.g., epilepsy) are common	About 1%

IQ, intelligence quotient