Thursday, December 31, 2009

1 in 86: the prevalence of autism among adults

This post was chosen as an Editor's Selection for
"Autism rate in children has doubled, say doctors" ... "Autism 'more common than thought'" ... "Autism in children '10 times higher' than first thought" ... "Autism at a record high" ... "autism is 25 times more common than what researchers thought"...

This mess of headlines and claims was generated in response to one autism prevalence study, Baird et al. (2006), published in the Lancet.

All 56,946 individuals comprising the targeted population cohort in this study are, as of today, the last day in the decade, 18 years of age or older. They were born between July 1, 1990 and Dec 31, 1991 and they are now all adults.

Within this cohort, Baird et al. (2006) reported an autistic spectrum prevalence of ~116/10,000. That's 1 in 86, and all these autistics, originally assessed as such when 9 to 14yrs old, are now adults.

For those to whom this is a matter of pressing importance, Asperger's contributed exactly nothing to that prevalence figure. So none of those 1 in 86 assessed-as-autistic now-adults are, at least according to Baird et al. (2006), Asperger's.

I've previously rattled on about Baird et al. (2006), one of the most important autism epidemiological studies to be published to date, and one of the most misrepresented. The authors found that small differences in case definition produced prevalence figures ranging from ~25/10,000 (1 in 400) to ~116/10,000 (1 in 86), a 4.6-fold discrepancy--within the same cohort at the same time, using the same diagnostic criteria, diagnostic team, and "gold standard" diagnostic instruments.

In the context of an earlier closely related prevalence study (Baird et al., 2000), the authors additionally found that a change in case ascertainment method doubled autistic spectrum prevalence within very nearly the same cohort, even when diagnostic standards were equivalent.

But such provocative and crucial findings, and others similar, were lost in the predictably incoherent uproar (see representative headlines and quotes, above) over that one figure--the 1 in 86 who as of today are all adults. I suggest that if Baird et al. (2006) had been conducted in exactly the same manner with a cohort born five years earlier, the findings would not be much different. Or ten years earlier, or more, were that possible. Of course that's a wild guess, but not an entirely unfounded one.

Earlier this year, a small innovative UK study reported a prevalence of about 1 in 100 for autistics aged 16 and up--for autistic adults right up to and over age 75. There are only bad reasons for why this small study of autistic adults is unique and unprecedented.

The world would look very different now, for both autistics and nonautistics, if over the past decade or more there had been a rational discourse about autism prevalence in which the existence of older autistics was not automatically denied.


Baird, G., Charman, T., Baron-Cohen, S., Cox, A., Swettenham, J., Wheelwright, S., & Drew, A. (2000). A screening instrument for autism at 18 months of age: a 6-year follow-up study. Journal of the American Academy of Child and Adolescent Psychiatry, 39, 694-702.

BAIRD, G., SIMONOFF, E., PICKLES, A., CHANDLER, S., LOUCAS, T., MELDRUM, D., & CHARMAN, T. (2006). Prevalence of disorders of the autism spectrum in a population cohort of children in South Thames: the Special Needs and Autism Project (SNAP) The Lancet, 368 (9531), 210-215 DOI: 10.1016/S0140-6736(06)69041-7


DifferentlyWired_10 said...


These prevalence studies are seriously flawed because they don't include Asperger's Syndrome, a neurological disability that is ON the Autism SPECTRUM.

Asperger's IS a disability and should be included in any and ALL prevalence studies. I have an Asperger's diagnosis, and I wonder why other people with the same diagnosis are excluded from prevalence studies.

I think Michelle Dawson et al. should take the Autism SPECTRUM seriously. I am extremely disappointed to see people like Ari Ne'eman and myself excluded from prevalence studies.

Please explain why exclusive prevalence studies were done. Please explain why Michelle chose to publish exclusive prevalence studies that do not include ALL persons with Autism disorders?


Katie K.

DifferentlyWired_10 said...


"The world would look very different now, for both autistics and nonautistics, if over the past decade or more there had been a rational discourse about autism prevalence in which the existence of older autistics was not automatically denied."

Does "the existence of older autistics" exclude older adults who were diagnosed with Asperger's as children such as Alexander Plank, Katie Miller, etc.?

Does "the existence of older autistics" exclude older adults who were who were diagnosed with Asperger's as adults such as John Elder Robison, Temple Grandin, Jerry Newport, etc.?


Katie K.

Unknown said...

I think the inclusion or exclusion of Asperger probands is a red herring. I suspect that a similar study that *did* include AS probands would lead to the same very important implications, regarding both the extent of autism spectrum conditions into adulthood, and the huge effect that small variations in case definition and case ascertainment have on the numbers.

And I agree with Michelle that were these implications given the exposure and mindshare they should have had, the public discourse about autism would be very different.

Michelle Dawson said...

Generally in response, I suggest reading both Baird et al. (2000) and Baird et al. (2006), the two papers I cited. Both papers briefly explain the problems the authors encountered in diagnosing Asperger's and what in consequence was done in each study.

Many researchers are disinclined, for one reason or another, to diagnose Asperger's as distinct from autism. There is no current consensus as to how exactly to diagnose Asperger's (see Klin et al., 2005, for three different methods, and there are more).

Neither "gold standard" diagnostic instrument (both are used in Baird et al., 2006) comes with Asperger-specific criteria. The ADI-R has only one set of cut-offs (for autism) and the ADOS has two (autism and ASD).

Most Asperger individuals also meet DSM-IV and ICD-10 criteria for the specific diagnosis of autism. Peter Szatmari has commented on this well-known problem. The DSM-IV further requires that if autism can be diagnosed, it must be (the priority rule).

I'm affiliated with a lab where autism and Asperger's are considered distinct, at least for now (meaning, this may change) and at least for many research purposes. But in the work I've been involved in, very nearly all Asperger individuals have met DSM-IV autism criteria as well as autism cut-offs on the ADOS and ADI-R.

"DifferentlyWired_10" might be "extremely disappointed" to be lumped in with autistics like me, but this happens a lot in autism research for the above reasons, among others.

By the way, Temple Grandin does not, according to her own report, have an Asperger's diagnosis.

Stephanie said...

"Most Asperger individuals also meet DSM-IV and ICD-10 criteria for the specific diagnosis of autism. Peter Szatmari has commented on this well-known problem. The DSM-IV further requires that if autism can be diagnosed, it must be (the priority rule)."

Asperger's is often diagnosed in people who are high-functioning, regardless of whether or not they meet the criteria for autism.

I was diagnosed with Asperger's once merely for being high-functioning even though I have been diagnosed with "autistic disorder" previously.

But I understand this reasoning because I am certainly nothing like a non-verbal adult or someone who does not have the intellectual ability I do.

So, it seems to be a way of saying that they currently function more like a person with Asperger's rather than what is usually thought of as autism, regardless of history (I had a speech delay, etc.)

A person with high-functioning autism will benefit from the type of treatment for those with Asperger's rather than for someone who does not communicate in any way.

It just looks like a way of classifying people into "functioning" categories, not separate autism disorders.

Michelle Dawson said...

I agree with Ms Keil's observation that autistics are often ranked, classified, etc., according to perceived or presumed outcomes.

But I disagree that ranking and classifying (and writing off) autistics this way has anything approaching an adequate scientific basis. There are also major ethical problems.

Also, I suggest that anyone here using terms like "high-functioning autism" provide criteria, instruments, thresholds, etc.

For perspective, less than 1% of the general population has Ms Keil's reported (by her) intellectual ability.

EquiisSavant said...

Another significant problem no one likes to talk about is classifying people with Autism according to how they can communicate. Is a person who cannot communicate with telephones, paper print, and usually not in-person low functioning ?

What if the person is an autistic savant, has a Juris Doctorate degree, can write a White House level legal brief, but cannotcommunicate with telephones, paper print, and usually not in-person, but requires Internet computer formats and a speech recognition device ?

I am just asking, because there seems to be a huge degree of misconception out there about what we autistic savant can and cannot do.

EquiisSavant said...

apologies for the typos -- hubby was wanting attention, and I cannot divide my attention when there social things happen.

Michelle Dawson said...

This post was chosen as a ResearchBlogging Editor's selection.

Unknown said...

This statistic is not accurate. The CDC confirms that the autism rate is now 1 in 110. Previously, in 2007 the CDC reported a prevalence of 1 in 150. There are alternate reports that show a higher rate, but these findings indicate self reported information.

Michelle Dawson said...

The multi-city CDC studies are not the only available prevalence studies of autism, nor necessarily the best designed. And not everyone lives in the US.

Also the CDC studies do not involve direct assessment of any individuals. This contrasts with Baird et al. (2006) which involved some direct assessment. This information can be found in the respective studies as well as by following a link I provided in the original post.

What I wrote can generally be verified by reading Baird et al. (2006). Also, the prevalence study in adults, published in 2009, is available via the provided link in the original post.

Heather said...

Dear Michelle,

My son was recently diagnosed with ASD and Mental Retardation to be ruled out over time. He is 4-years-old. We live in California.

My question to you is this: How would you suggest we learn to communicate in a mutually understood language so we can respond to each other appropriately?

His step-father and I home educate him as best we can and are not (at this time) participating in ABA therapy. My son's level of anxiety is high and I am now certified to give him therapeutic massage, which he seems to enjoy immensely. My son and I share a wonderful bond, although it hurts me to see him so frustrated with communication and socializing.

If you had a child with Autism, how would you handle these daily hurdles? What were the challenges you faced as a minor while dealing with being "different"? Would you be willing to help educate parents, therapist, etc?

What should we be doing to help these children function in our world? The ethical treatment of people with Autism is mandatory, of course, as is ethics when participating with anyone who is labeled "different" by some standard. We believe the way to understanding our son is through education. Since you have Autism and can communcate well, do you have any insights on better techniques to help our child?

The only thing I wish for in my son's life is for him to find a way to be happy. I love him and I would never put him in an institution because he is an integral part of my life, just as I am in his. I understand that the facts just may indicate he'll be with me forever and that's okay too.

I just want to be able to understand his needs and desires so we can live in harmony.


Heather M.

Michelle Dawson said...

In response to Heather, the only advice I can give is to suggest that *anyone* interested in the well-being of autistics should seek out as accurate information about autism, and about approaches to autism, as is currently possible.

Sadly, this is much more difficult than it should be. It requires very good critical thinking abilities. It requires sorting through reams of false and harmful information.

One thing I found helpful was to read about the standards applied to nonautistic people in intervention and treatment research.

There is a lot of good popular-level writing about this (you can find some in my links, like the James Lind Library). These evolving standards of science and ethics exist because without them, people were harmed.

Anyone who is concerned about the well-being of autistics (whether one individual autistic or autistics as a group) should look for these basic standards in everything they read about autism and approaches to autism.

Mark Erickson said...

Hello, thanks for the blog, I enjoy reading it.

I recently got dragged to a therapy "seminar" for an autism treatment provider. PACE Place. One thing mentioned was Polyvagal Theory, by Stephen Porges.

Any one heard about these? I'd appreciate it.

Ella said...

Hello I'm Ella, Iman's mother. My son, Muhammad Tajul Iman was born on 15th June 2003. He was like a normal boy when he was born until he was up to 2 years. We noticed something not right in him. He's physically normal, but there are a few things that makes us so worry. When he was 2 1/2 year old, we referred him to the Hospital as I noticed my son always knocked his head for no reason. Also, I noticed he was not able to speak or communicate with us thoroughly, no eye contact, and temper tantrums. After a series on treatment and follow up, the Doctor at HUKM diagnosed him to have Autism and ADHD (Attention Defisit Hyperactive Disorder) problem. Please welcome to my son blog

Leo Leonidas, MD said...

Hi Michelle, I just wonder if you have looked into the possibility of sub-clinical hypothyroidism as a possible cause of the signs of Autism.

I have seen studies that many pregnant moms lack iodine in their diet.

Leo Leonidas, MD