This is the 2007 version. Click here for the 2017 chapter 12 table of contents.

Categorization of Intellectual Disability

In addition to providing a place to note personality disorders (described above) and defense mechanisms (described in Chapter 11, p.517), Axis 2 of DSM-IV provides a place to note severity of mental retardation, or intellectual disability as it is now called.

About 1 in 10 American families has a mentally retarded family member. (McLeod, 1985). Words used to describe cognitive impairment have changed over the years. Each set of terms is abandoned when it takes on insulting connotations. Terms like idiot and moron once served as diagnostic categories, referring to different degrees of impairment.

How were the terms idiot and moron originally used?

Ever since the Stanford-Binet intelligence test or "IQ test" was published in 1916, IQ tests have been used to assess the abilities of disabled individuals. The IQ is calculated using this formula:

IQ (intelligence quotient) = 100 x Mental Age / Chronological Age

If a child of 10 performed like a 7 year old, when tested, he or she would be assigned an IQ of 70 (100 x 7/10).

In the 1920s, an idiot was defined as a person with an IQ in the range of 0 to 30, an imbecile was a person with an IQ between 30 and 50, while a moron had an IQ between 50 and 70. In DSM-IV, by contrast, the following terms and criteria are used:

Mild Mental Retardation IQ level 50-70

Moderate Mental Retardation IQ 35 to 50

Severe Mental Retardation IQ 20 to 35

Profound Mental Retardation IQ below 20

The label "Mental Retardation, Severity Unspecified" is used when a person is clearly mentally retarded but cannot be tested. . Perhaps inevitably, the phrase mentally retarded is now on the way out. The American Association on Mental Retardation changed its name in 2006 to the American Association on Intellectual and Developmental Disabilities. DSM-V when it comes out will probably refer only to intellectual disabilities or cognitive impairment, not mental retardation.


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