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Autism Disorders and Intellectual Disability: Claim that 75-80% of Persons with Autistic Disorder are Intellectually Disabled i

Posted May 03 2010 2:41am
As I mentioned in my previous post Alan Griswold of Autistic Aphorisms is one of those comfortable with speculation that Jesus Christ may have been autistic but is not comfortable with the fact that many persons with Autistic Disorder are Intellectually Disabled.  Mr. Griswold and Astrid at at  Astrid's Journal disagree with my numerical references and wrongly describe them as self constructed.

My claim is not that 75-80% of all persons with an Autism Spectrum Disorder are also Intellectually Disabled as Astrid in particular seems to think. My assertion is that credible authorities have stated that 75-80% of persons with Autistic Disorder are intellectually disabled.  I stand by that assertion and, once again, for those who actually read before reacting, offer the sources
1. Canadian Psychological Association    Autism Brief to the Standing Senate Committee on Social Affairs, Science and Technology November 9, 2006.

In that brief the CPA refers to 2 separate categories "Autism" and Asperger's"
"Cognitive impairment is present in about 80% of persons diagnosed with Autism and
general intellectual functioning is most often below average
. Persons diagnosed with
Asperger’s Disorder have average to above average intellectual functioning.


In sum, persons with ASD present with a wide range of impairments in cognition, language and
behaviour which present in some common but reliably distinct ways between Autism and
Asperger’s disorders

2. Center for Disease Control Counting Autism 

CDC’s most recent data show that between one in 80 and one in 240 children with an average of one in 110 have an ASD. This is a prevalence of about one percent of children. These results reflect data collected by CDC’s Autism and Developmental Disabilities Monitoring (ADDM) Network in multiple communities throughout the U.S. in 2006.

Estimates are based on health and education records from participating communities, which includes eight percent of the U.S. population of eight year olds. All children in the studies were eight years old because previous research has shown that most children with an ASD have been identified by this age for services.


Cognitive Functioning (from the pdf version)


From 37.9% (Arizona) to 63% (Alabama) (overall average: 43.8 %) of the children identified with an ASD also had an intellectual disability (an IQ ≤70, at the sites that had test results on intellectual ability for at least 75% of the children identified).


From 29.3% (Colorado) to 51.2% (South Carolina) (overall average: 41.0 %) of the children identified with an ASD also had an intellectual disability (an IQ ≤70, at the sites that had test reults on intellectual ability for at least 75% of the children identified)

The CDC figures of 41-44% for all persons on the Autism Spectrum having an intellectual disability are consistent with the 80% figure for those with Autism EXCLUDING Aspergers cited by the CPA. These figures and sources are my authorities for the upper end of the 75-80% range of persons with Autistic Disorder having an Intellectual Disability.  That is not a self constructed figure.
The lower end of the range I cite is the figure based on older sources like the 1992 ICD diagnostic criteria for Autism:
3. The ICD-10 Classification of Mental and Behavioural Disorders World Health Organization, Geneva, 1992

F84.0 Childhood Autism

A pervasive developmental disorder defined by the presence of abnormal and/or impaired development that is manifest before the age of 3 years, and by the characteristic type of abnormal functioning in all three areas of social interaction, communication, and restricted, repetitive behaviour. The disorder occurs in boys three to four times more often than in girls.


All levels of IQ can occur in association with autism, but there is significant mental retardation in some three-quarters of cases.

F84.1 Atypical Autism

A pervasive developmental disorder that differs from autism in terms either of age of onset or of failure to fulfil all three sets of diagnostic criteria. Thus, abnormal and/or impaired development becomes manifest for the first time only after age 3 years; and/or there are insufficient demonstrable abnormalities in one or two of the three areas of psychopathology required for the diagnosis of autism (namely, reciprocal social interactions, communication, and restrictive, stereotyped, repetitive behaviour) in spite of characteristic abnormalities in the other area(s). Atypical autism arises most often in profoundly retarded individuals whose very low level of functioning provides little scope for exhibition of the specific deviant behaviours required for the diagnosis of autism; it also occurs in individuals with a severe specific developmental disorder of receptive language. Atypical autism thus constitutes a meaningfully separate condition from autism.

* atypical childhood psychosis
* mental retardation with autistic features
These three authorities are the primary sources for my assertion that 75% (3/4 in the ICD) to 80% (CPA, CDC) of persons with Autistic Disorder also have intellectual disability.  Those are not self constructed figures as claimed by Alan and Astrid.  They are figures provided by credible authorities.

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