Another Look at Intelligence and Autism

One of the things that gets bandied about with regular frequency is the proportion of severely impaired individuals on the spectrum and the accompanying rates of ID. I've run across another study that looks at both of these things. Chakrabarti and Fombonne (2001) found in a sample of 97 individuals with a pervasive developmental disorder: "A total of 97 children (79.4% male) were confirmed to have a PDD. The prevalence of PDDs was estimated to be 62.6 (95% confidence interval, 50.8-76.3) per 10 000 children. Prevalences were 16.8 per 10 000 for autistic disorder and 45.8 per 10 000 for other PDDs. The mean age at diagnosis was 41 months, and 81% were originally referred by health visitors (nurse specialists). Of the 97 children with a PDD, 25.8% had some degree of mental retardation and 9.3% had an associated medical condition."

I'll include interesting snippets from the study:

"The sample included 77 boys (79.4%) with no significant difference ({chi}22 = 0.33; P = .85) in the proportion of boys in the AD (76.9%), Asperger syndrome (84.6%), and PDD-NOS (80.4%) groups. Of the 97 children, 29 (29.9%) had no functional use of language defined as the daily spontaneous use of 3-word phrases. The proportion of children without functional language was however strongly associated with diagnostic subtype (AD, 69.2%; Asperger syndrome, 0%; PDD-NOS, 16.1%; {chi}22 = 30.6; P<.001)."


Only a third of the sample had "no functional use of language."

A fourth of the sample had "some degree of mental retardation."

Not surprisingly, a "significant difference was found for the presence or absence of mental retardation between the 3 PDD subtypes ({chi}22 = 40.6; P<.001), the AD group having more frequent and severe cognitive delays than the Asperger syndrome and PDD-NOS groups."

There are folks in the autism community that insist there's an epidemic and we're fixing to be hit with a tidal wave of nonverbal, diapered adults, but this does not seem to be the case:

"In our survey, AD accounted for only 27% of the cases with these children showing much greater cognitive and language impairments. By contrast, the majority of cases was found at the mild end of the autistic spectrum, with the PDD-NOS and Asperger syndrome groups accounting for 71.1% of the cases. High proportions of PDDs were also found in recent surveys (46.8%18 and 40%19). Prior surveys focused on a narrow definition, which led to the exclusion of these milder forms although it has been recognized for some time that they represented a group as sizable if not bigger than that of autism.5 The inclusion of these milder variants certainly may account for a substantial part of the increase in prevalence rates."

Contrary to this fantastical and fanatical assumption that most individuals with autism are severely disabled, incapable of speech, etc., the reality appears to be that a loosening in diagnostic criteria that allows for the diagnosing of many more individuals with less severe impairments had occurred. Now, this study's been out there for nine years. I've said before, and I'll say it again here, research is poorly disseminated to the public. I'll go a step further, here, and say that is almost as poorly disseminated to the clinicians and practitioners who diagnose and treat autism. These discrepancies between what researchers know and what practitioners, clinicians, parents, and the public know are widening, not lessening. This is frightening, and undoubtedly accounts for all manner of misinformation and woo to abound.


Chakrabarti S, Fombonne E (2001). "Pervasive developmental disorders in preschool children". JAMA 285 (24): 3093–9. doi:10.1001/jama.285.24.3093. PMID 11427137. http://jama.ama-assn.org/cgi/content/full/285/24/3093.


farmwifetwo said...

I think linking ID/MR to autism sets a dangerous precidence - why should we teach them if they'll amount to nothing anyways - and I'm glad it won't be on the V... This from a parent who's 8yr old has an IQ score (Feb 2010) of 60 to 70.

Ironically, contrary to Harold's probable answer of "told you so", not one of my professionals wants to hear that number. The Ped, the Psychometrist that did the testing nor the Special Ed guy that's found us an amazing slow learners classroom.

Why?? B/c it's been well documented that the IQ test is inappropriate in showing levels of knowledge in those with autism. Nor does it tell you how far a child with autism may develop and learn.

The rest of the testing read "Reading, Gr 3.5, Comprehension Gr 1.5, Math K". My son had spent an hour alone with a stranger. The psychometrist's response when he did this testing with us... "if you can get his comprehension and communication skills (computer, speech etc) up... He'll do amazing".

When I asked him of he would qualify for the slow learners not the ID/MR stream in h/s... The response "definately".

His IQ score says he's as smart as a 2 to 3 yr old... Nobody else believes it to be true... Except for Harold who seems to be fixated on the number.

Our paperwork now reads "Communication - Autism", "Intellectual - Dev Delay" There's nothing wrong with a double dx... especially when it keeps you out of the ID/MR/ASD classrooms and puts you in with those that just need a little extra attention.

Nic said...

My son is severely autistic with severe learning needs as well (ie one of the mass of future adults who are going to cause a meltdown in service provision). Since he started at his special school at age 2 (9 years ago) the number of children with similar needs have remained steady, at approx two kids per year in our Local Authority.

I have no idea where all these highly dependent children are that they talk about. They certainly don't exist where I live.

Roger Kulp said...

I would be curious how,if at all, learning disabilities fit into this.While we don't have MR/ID,my sister and I have struggled all our lives,with serious learning disabilities.

It is interesting to note how few parents of autistics with serious ID besides Harold have blogs.Given all the woo out there about this,there would be dozens at the least.

It is looking more and more like my autism,developmental problems , and and many of my medical problems are due to a previously undiagnosed congenital/maternal infection,cause of autism that can be prevented by vaccines.

It would be interesting to know what per centage of autism has this as a cause.

Joseph said...

I mentioned that study here. It's in line with other studies. It should go without saying, but the 70% MR stat that is usually brandied about is rather outdated.