Definition of Intellectual Disability


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What two (2) major elements are necessary for a diagnosis of mental retardation?

Intellectual disability is a disability characterized by significant limitations both in (1) intellectual functioning and in (2) adaptive behavior, which covers many everyday social and practical skills.  (American Association on Intellectual and Developmental Disabilities [AAIDD], 2010 , para. 1)

What are the limitations of this definition?

The first and most objective limitation is the age of onset.  This disability originates before the age of 18.   (AAIDD, 2010 , para. 1)

A second quasi-objective limitation to a diagnosis of mental retardation is intelligence quotient (IQ).  One criterion to measure intellectual functioning is an IQ test.  Generally, an IQ test score of around 70 or as high as 75 indicates a limitation in intellectual functioning.  (AAIDD, 2010 , para. 3)

A third, more subjective measure, is the degree to which a disability limits adaptive behavior.  Standardized tests can be used to gain objectivity in the areas of conceptual, social, and practical skills.

Fourth and finally, the AAIDD takes qualitative differences in environmental, cultural, socioeconomic, and other normative factors (language) into consideration.  They acknowledge that limitations often coexist with strengths, and that outcomes can be positive with sustained personalized supports.

How does this definition compare to the DSM-IV TR?

The DSM-IV-TR criterion(s) for a mental retardation diagnosis are as follows… (American Psychiatric Association, Diagnostic and statistical manual of mental disorders, 2000, p. 41)

A)    Significantly sub-average general intellectual functioning accompanied by;

B)    Significant limitations in adaptive functioning in at least two of the following skill areas:

  1. Communication
  2. Self-Care
  3. Home Living
  4. Social/Interpersonal Skills
  5. Use of Community Resources
  6. Self-Direction
  7. Functional Academic Skills
  8. Work
  9. Leisure
  10. Heath
  11. Safety

C)    The onset must occur before age 18.

The DSM authors make more formal recommendations on which IQ tests should be used to measure IQ and acknowledge differences of measurement between them.  They share commonality with the AAIDD definition in the regard to the arbitrary IQ cutoff (approximately 70-75 or below).  The DSM also shares concern with AAIDD in that they “take into account factors that may limit test performance (e.g., the individual’s socio-cultural background, native language, and associated communicative, motor, and sensory handicaps). (4th ed., text rev.; DSM-IV-TR; American Psychiatric Association, 2000, p. 42)  Like the AAIDD, the DSM posits a dimensional assessment of strengths and weaknesses when the nature of the disability skews IQ scores.

Although I think the variance in severity is implied by the AAIDD, the DSM authors codified the broad differences between individuals with mental retardation.  On the whole, my impression is that the AAIDD definition was written and based on the DSM-IV-TR.


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References

American Association on Intellectual and Developmental Disabilities. (2010 ). Definition of intellectual disability. Retrieved March 26, 2010, from http://www.aamr.org/content_100.cfm?navID=21

American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders (4th ed., text rev.). Washington, DC: Author.

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