Number Issues: Autism and Intellectual Disability

"Another difference between past and present autism diagnosis involves the presence of intellectual disabilities, adds Yeargin-Allsopp. During the 1960s and 1970s, the vast majority of those diagnosed with autism had an intellectual disability but today, only about 40% have one." --from CMAJ

This does not equate to an 80% figure of ID for those with autistic disorder, no matter how one parses the numbers. In fact Yeargin-Allsop's 2003 study disconfirms the idea that most individuals with the AD diagnosis have ID. Some individuals are fond of the 80% number for ID and autism comorbidity (like others are so fond of the 80% divorce rate, also untrue).

The CDC's press briefing on the latest autism findings offer this:

"Catherine Rice:  So in terms of mental retardation, it's now more commonly referred to as intellectual disability.  We know there's quite an overlap in intellectual disability and autism spectrum disorders.  For many years, the best statistics and disorders told us 75% or three-quarters of children with autism also had an intellectual disability.  Now the numbers that we're identifying in our study shows us it's more about 40% or more specifically 41% of children with autism having an intellectual disability.  So overall, this is a population with less intellectual impairment, sometimes referring to as more a higher functional population.  So there are many theories out there in terms of this diagnostic shifting and how we look at things or are we really seeing a more high functioning population?  That is challenging to sort out."

In an earlier post, I covered the latest findings regarding ID and autism:

Yeargin-Allsopp et al. (2003) write: "Children with autism were identified as part of the Centers for Disease Control and Prevention's (CDC) Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP), an ongoing, active population-based surveillance program to monitor the occurrence of 5 DDs (autism, cerebral palsy, hearing loss, mental retardation [MR], and vision impairment) among 3- to 10-year-old children in the 5-county metropolitan Atlanta area.25-26 The total number of 3- to 10-year-old children residing in metropolitan Atlanta in 1996 was 289 456 (51% male; 58% white, 38% black, and 4% other racial group)."

According to Yeargin-Allsopp et al. (2003), "Psychometric data were available for 880 (89%) of the 987 children with autism. Of these, 676 (77%) had been administered a standardized intelligence test, and the others had received a developmental test (a list of psychometric tests is available from the authors). Children with a full-scale IQ of 70 or less or a score of 2 or more standard deviations below the mean on the cognitive domain of a developmental test were classified as having a cognitive impairment."

So what did Yeargin-Allsopp et al.find?: "Among the children with autism (N = 987), 62% had at least 1 coexisting MADDSP-defined disability or epilepsy. Of the children with an IQ or developmental test result (N = 880), 68% had cognitive impairment (64% based on IQ data alone). Among children with psychometric test data (N = 880), 20% had mild MR, 11% moderate MR, 7% severe MR, 3% profound MR, and 28% with an unspecified level of cognitive impairment that included 9% classified as MR-NOS using IQ data and 19% classified using developmental scores (Table 2). In addition, of the children with autism, 8% had epilepsy, 5% had cerebral palsy, 1% had vision impairment, and 1% had hearing loss. We found that as the severity of MR increased the sex ratio decreased (4.4 to 1.3), indicating a greater proportion of females in the severe and profound levels of impairment (Table 2)."

In other words, about two-thirds had a cognitive impairment, but of those most were mild cases, not severe. Standardized IQ tests for autistic individuals have potential problems; it can be tremendously difficult to ascertain capability from a noncompliant individual. In addition, since language deficits are part of the autism triad, the verbal portion can be expected to be lower than nonautistic peers, and it does not appear that the nonverbal IQ test is always (or often administered) in place of the traditionally used IQ test. Where noncompliance, lack of inherent interest, difficulty with communication, and discomfort with strangers can all get in the way of a reliable test result, IQ tests must be taken with a grain of salt, especially where performance outside the testing arena demonstrates more competency than the IQ score would have predicted.

Individuals with autism are likely to have additional diagnoses, as well: "Many children (70%) we identified with autism had more than 1 diagnostic evaluation, and 61% (data not shown) were seen at more than 1 educational or medical program in the community, thus providing independent information on the behaviors used to determine case status."

Scientists aren't in agreement with an 80% rate of ID in autistic individuals. In fact, the findings show that only 7% of those with autism are severely intellectually disabled. The overwhelming majority who have ID have mild to moderate ID. Many individuals with mild ID are able to live independent lives. Having autism comorbid with ID makes full independence more challenging, but it is the autism that creates this impediment, not the ID.

The portrait of autism has changed over the last forty years. More mildly affected individuals are being diagnosed with autism spectrum disorders as our awareness and understanding of autism has grown.

Most of those diagnosed with autism are not severely disabled. That doesn't mean that severely impaired individuals who require 24/7 care shouldn't be acknowledged and recognized. But restricting autism to this minority isn't going to happen.

Like it or not, our understanding of autism has broadened to include those on the broader autism phenotype who have less significant barriers. Personally, as the mother of three children who have tremendous commonalities with each other despite the variation in severity of the autism and the variation in intellectual impairment (my son has an intellectual disability but my daughters give every indication of being gifted), I respect and appreciate the increased awareness. Individuals who are extremely bright may still face significant challenges and have impairments that impede their ability to live independently.

Trying to manipulate numbers to fit one's notion of autism as also being intellectual disability is not scientifically accurate, and the historical numbers of 70% or so were based not on sound science and replication, but on taking a few original studies and their interpretation of 70% and carrying it forward in time rather than measuring the IQ of the study participants. In other words, it was a readily accepted and rarely questioned axiom that ID and autism went hand-in-hand. Assessing the IQ in noncompliant individuals (as many autistic individuals can be) is a difficult enterprise, so previous studies' assessments were used.

Times have changed, though, as our awareness and willingness to question have increased. Scientists now assess IQ. Recognition that traditional IQ testing may not best assess capability has also grown. Remember, IQ as assessed by the WAIS-III and Stanford-Binet assess the likelihood of success at academic performance. If a person hasn't had the kind of instruction or exposure to those kinds of material, he will not score well. It doesn't tell us about functional life skills. It doesn't tell us about the ability to hold a job, live semi-independently, socialize appropriately.

These changes in how we view and assess autism are good things. Whether the APA gets their act together and manages to put together a severity scale that is useful without pejorativeness is another matter entirely, as is the willingness of interested members of the autism community to accept communally drawn definitions of autism based on the scientific research.


Yeargin-Allsopp, M., Rice, C., Karapurkar, T., Doernberg, N., Boyle, C., & Murphy, C. (2003). Prevalence of Autism in a US Metropolitan Area. JAMA: Journal of the American Medical Association, 289(1), 49. Retrieved from Academic Search Complete database.


farmwifetwo said...

Harold's on the bandwagon and I haven't figured out why b/c he won't say except that he did post a few posts back that he wants his kid in a room in a residential facility.... YUCK!!!! He doesn't want him in a group home and he's upset there aren't enough facilities for him to choose from.

I suspect their 80% ID rate may be close... if you only used IQ scores... My little man's score is in the 60's and he's 8.5. But I was told to ignore it, by the psychometrist, the ped and even special ed... Ironically b/c he reads at grade level he actually doesn't qualify for the spec ed class I'm putting him into next year. He's going b/c comprehension and math are 2 and 3 yrs delayed... AND... b/c she pedals speach... She doesn't care how, what medium, the number of words... and we need that. Yes, we have verbal mands, yes I even has basic joint attention - which is getting more and more often. BUT, he doesn't "talk". Everything is triggered by a "want", a "need", a "b/c it's happening now" or "B/c I saw it on the calendar". I want "just b/c, little boy initiated talking and someone else initiated a topic and just/b little boy had a comment to make" - speach... one word, 3 words... I'm not fussy. Just easy... not slamming up against those bends and breaks in his brain.

The psychometrist already told me he qualifies for the ID educatable stream in h/s. Must be Gr 3/4 level... IQ test says he'll never learn....

This Mom says... let's take the psychometrists advice... "teach him to talk, teach him comprehension... who knows how far he'll go"....

They can shove the IQ test... I'm aiming to have one of those non-verbal children who magically starts to talk at puberty... Harold can shove his "out of sight, out of mind", if he wants.

I have no use for ABA... been there did that for a year. Harold loves ABA.... Who's child... with the same dx... same IQ level... is doing better??? Mine goes everywhere... his has difficulty traveling... Mine takes part in swimming lessons, was in a regular classroom and will return anytime btwn now and definately in Gr 7 depending if or how quickly he starts to talk... His was being taught alone in a small room...

You'll never convince me either of the "wonderfulness" of ABA.

"Grendel" said...

Kwombles - thank you for that post it has been very thought provoking and the links will be useful - policy makers need an update on the research!

Autism Reality NB said...

Thank you for offering a counter opinion.

My reference to the 80% figure is a reference to those with Autistic Disorder not all persons with Autism Spectrum Disorders. I have two primary sources for that view:

1) The Canadian Psychological Association 2006 brief to the Canadian Senate Committee which was studying autism and the studies referenced therein. That brief distinguished between "autism" and Aspergers and stated that 80% of those with Autism have cognitive deficits.

2) The 2004 and 2006 CDC surveys which found that persons with autism spectrum disorders also had intellectual disabilities in 44% of instances (2004) and 41% (2006). Estimates of 40% + for the entire autism spectrum which includes the many with Aspergers who, by diagnostic definition, do not have intellectual disability are consistent.

I am sorry that you KWombles and FW2 are offended by association of Autistic Disorder and Intellectual Disability. Your hostility towards that reality will not change it.

You may not be happy to learn of the recently reported study reporting Evidence of Common Genes Linking Autism Spectrum Disorders and Intellectual Disability.


FW2 the truth is not a "bandwagon".

KWombles said...


I'm aware of that study.

You're arriving at the 80% incorrectly by assuming there is an even split between autistic disorder and the four other diagnoses within PDD and doubling the rate. This is incorrect.

Intellectual disability is not a requirement of autistic disorder. Not everyone diagnosed with autistic disorder has ID. I have two children with that diagnosis. One has an ID because of a stroke (in other words he had the AD diagnosis before the stroke and without accompanying ID) and one has no ID.

You're missing the point. I'm not hostile about this. I'm relying on the science which is not in your favor.

If your intention is to maintain a focus on the most severely disabled individuals with autism and their need for greater resources to be allocated, inflating numbers and pulling a martyr act isn't the way to do it.

You keep putting words into people's mouths that they've not said. You want any credibility you should probably knock that off.

KWombles said...

"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."


The problem with this is that it is not substantiated and the literature assessing ID and autism clearly doesn't back this up.

It'd be like using Autism Speaks to back up the 80% divorce rate, something they still spread around despite the evidence to the contrary.

We should always be wary of generalizations not backed by scientific studies that provide the data to make those generalizations. The Canadian Psychological Association's references for that briefing are not reputable scientific articles:

"Autism Society Canada (2006). Focus on Change: An Open Letter From Autism Society Canada

Autism Society Canada (2006). Largest Collective Voice of the Autism Community in Canada
Calls on Government to Take Steps to Establish a National Autism Strategy.

Bryson, S. (2003). Autistic Spectrum Disorders: Recent Findings on Prevalence, Etiology
and Neuropsychopathology. Canadian Psychological Association Preconvention Workshop.
Hamilton, Ontario.

Jack, M and Ady, J. (2006). A Guide to Choosing Interventions for Children with Autism
Spectrum Disorders. Alberta Centre for Child, Family and Community Research.

Perry, A. and Condillac R. (2003). Evidence-Based Practices for Children and Adolescents
with Autism Spectrum Disorders. Review of the Literature and Practice Guide. Children’s
Mental Health Ontario."

It's shoddy work, at best.

farmwifetwo said...

It is a bandwagon when you go on and on about a topic but aren't willing to give a reason why you want government's to stop funding early interventions when you've been on that bandwagon for years as well.

So, what is it... should we write off all children that have been diagnosed as autistic disorder with IQ's at 60 when they are 2... stuff them into facilities Harold...

Or should we give them a chance.

I've voting for a chance. You can stuff yours into a residence... You can give up on that poor child who's barely starting his teen years. But then again he's been stuffed into a small room for years being trained using ABA and kept away from the rest of the children except under controlled conditions. So he's unable to handle the "real world"... or is that what's got you mad... They are going to move him out of it at highschool and put him in a special ed class and ABA will be done so by ranting about is ID you are attempting segregation at h/s as well??? Moreso than just a spec ed class??

I'm going to do my best to prove his autistic but smart. I'm aiming for independance, and treating him with respect. And mine... mine is going to do what he likes to do best "play with the children". Even if he hasn't got much of a clue how to do it.... but his friends don't care, they've been teaching him how.

They were just amazing at their "swim to survive" program a week ago at the pool. It's one thing to be told it... it's another to watch them. They just don't care.... he's one of them, that's all that matters to them. We're going to miss them... but he'll be back in Gr 7.

Also, at his new school during the recess we were there when we visited he had his cousin and another child come to see him... the other child was with him in swimming lessons... He'll make more friends.

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