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Defining Criteria for Intellectual Disability

Intellectual Disability


Intellectual Disability

Intellectual disability is a condition characterized by significant limitations in both intellectual functioning and adaptive behavior that originates before the age of 22.

Intellectual Functioning

Intellectual functioning—also called intelligence—refers to general mental capacity, such as learning, reasoning, problem solving, and so on.

One way to measure intellectual functioning is an IQ test. Generally, an IQ test score of around 70 or as high as 75 indicates a significant limitation in intellectual functioning.

Adaptive Behavior

Adaptive behavior is the collection of conceptual, social, and practical skills that are learned and performed by people in their everyday lives. 

  • Conceptual skills—language and literacy; money, time, and number concepts; and self-direction.
    Social skills—interpersonal skills, social responsibility, self-esteem, gullibility, naïveté (i.e., wariness), social problem solving, and the ability to follow rules/obey laws and to avoid being victimized.
  • Practical skills—activities of daily living (personal care), occupational skills, healthcare, travel/transportation, schedules/routines, safety, use of money, use of the telephone.
  • Standardized tests can also determine limitations in adaptive behavior.

Age of Onset

The condition originates during the developmental period, which is defined as before the age of 22. Intellectual disability is one  of several conditions known collectively as developmental disabilities.

ID 12th Edition
Intellectual Disability: Definition, Diagnosis, Classification, and Systems of Supports, 12th Edition
Diagnostic Adaptive Behavior Scale (DABS)

Additional Considerations

AAIDD stresses that additional factors must be taken into account when assessing intellectual disability, such as the community environment typical of the individual’s peers and culture.

Professionals should also consider linguistic diversity and cultural differences in the way people communicate, move, and behave.

Finally, assessments must also assume that limitations often coexist with strengths in a person, and that an individual's level of life functioning will improve if appropriate, personalized supports are provided over a sustained period.

Only after a comprehensive evaluations can a clinician determine whether an person has intellectual disability and can professionals tailor effective individualized support plans.

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