The American Association on Intellectual and Developmental Disabilities defines intellectual disability (ID) as the following:

  1. Substantial limitations in intellectual functioning
  2. Significantly limitations in adaptive behavior consisting of conceptual, social, and practical skills;
  3. Originating before age 18 ( AAIDD, 2008)
  4. Intellectual disability is concerned with IQ measures, intellectual functioning, language development and social behavior.

The severity of ID has been summed up in the following table:

Severity IQ Range % of MR Characteristics
Mild 52-68 89 Usually live and work independently within regular community. Often have families.
Moderate 36-51 6 Capable of some semi-independence at work and in residence. As adults, many work in supportive environments and live with relatives or in community residences.
Severe 20-35 3.5 Capable of learning some self care skills and are not totally dependent. Some adults are able to work in supportive environment and live with relatives or community residences.
Profound 19 and below 1.5 Capable of learning some basic living skills but will require continual care and supervision. Often exhibit multiple handicap

Read about sub sections of Mental Retardation at:

Cognitive Difficulties Language Characteristics