Thursday, February 08, 2007

Moving Toward a New Consensus Prevalence of 1% or Higher

The current consensus prevalence of ASD is roughly 1 in 166 or 60 in 10,000, as widely known. I believe this is still an underestimate.

I should clarify that I do not really believe there's a "right" number for autism prevalence. It's sort of like asking what is the prevalence of "short" or what is the prevalence of "light skinned". It depends on the boundary, and the boundary in autism is subjective. I believe it is somewhat subjective even when the best diagnostic tools are used. The standard deviation boundary of mental retardation is an analogous boundary, yet probably a more objective one.

Nevertheless, it appears that when ASD is screened thoroughly in a population, or when there's a lot of awareness and good ascertainment, prevalence is found to be closer to 1%. This is not new. The following is what Lorna Wing and David Potter said on the subject as early as 1999.

Because we concentrated on the children with learning disabilities (IQ under 70) we saw very few with the pattern described by Asperger. We had to wait for the study by Christopher Gillberg in Gothenberg to find out how many children with IQ of 70 and above were also in the autistic spectrum. As described above, combining the results of these two studies gave an overall prevalence rate for the whole autistic spectrum, including those with the most subtle manifestations, of 91 per 10,000 - nearly 1% of the general population.


And then:

Kadesjö et al (1999) report a study in Karlstad, a Swedish town. Although this was small scale it was very intensive (over 50% of the 7 year old children seen and assessed personally by the first author). The study found a prevalence for all autistic spectrum disorders for all levels of IQ, of 1.21%!!! Children were followed up four years later and had the diagnoses confirmed.

(source)

I believe Kadesjö's personal assessment of 50% of 7 year olds in Karlstad is key to that finding.

More recently, Baird et al. (2006) found a prevalence of 1.16% in South Thames, UK. In this study the authors, again, looked for children with a possibly undiagnosed ASD. Note that children in this study were born between 1990 and 1991, before the bulk of what is referred to as the "autism epidemic" got started.

Finally, we have Fombonne et al. (2006) which found a prevalence of 1.076% among Kindergarten children (born in 1998) in Montreal, Canada. While there are fluctuations in the prevalence by birth year cohort in this study, there are no indications that prevalence is about to level off just yet.

Additional supporting evidence comes from Posserud et al. (2006) out of Bergen, Norway. The authors found that 2.7% of 7-9 year olds were high scorers in the ASSQ.

In adults, prevalence of ASD can also be 1% easily considering that in studies of the properties of the AQ Test about 2-3% of adults score above 32-33, the cut-off at which an ASD is considered possible.

35 comments:

  1. You know, as time has passed I feel that we're all, everybody, is a little autistic. Afterall you could describe autism [simplistically] as different wiring and human quirkiness has such a vast array of variety that there are smidges of autism scattered all over the place.
    I think that's why people can relate to autistic people precisely because of those spikes and oddities that aren't as odd as they first appear when you examine them more closely.
    Cheers

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  2. Wait a second - the consensus prevalence of autism is increasing? But isn't thimerosal exposure decreasing at the same time?

    Wow. How do you explain that? ;-)

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  3. anonimouse,

    one word, "Illuminati."

    Thanks, Joseph. It is important to emphasize that the prevalence of "the whole spectrum" probably is closer to 1%, otherwise, every paper that comes out with another 10 per 10,000 found will make it sound like the prevalence is increasing.

    60 per 10,000 (gasp)
    70 per 10,000 (GASP)
    80 per 10,000 (GASP GASP)
    90 per 10,000 (GASP GASP GASP)
    100 per 10,000 (collapse from exhaustion)

    I think Michelle Dawson pointed out that the study in South Thames included kids who might not have really fit on the spectrum, but had something vaguely similar. They had really pushed the envelope on "autism" as I remember.

    I don't think that everyone is a little autistic, McEwen. It's kind of like saying, "everyone is a little African American." By the time everyone is a little "African American" the definition of "African American" has been dilluted beyond recognition. We are all human. That's important.

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  4. Hmm, autism rates will prolly continue to rise.

    There are 7 million adults dxed MR. What were autistics dxed before autism was known to doctors?

    Then there are other dxes like schizophrenia...emotionally disturbed and whatever doc's decided 30 or so years ago.

    Bet there are many incorrect dxes out there...and it will take 10-20 years to really have an accurate count of how many people are spectrum.

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  5. Yes, I thought it was better to announce it preemptively like this than wait until someone like Rick Rollens comes along and says "the sky is falling! the sky is falling!"

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  6. Hey Joe, now you have to round up 1 in 100 76 year olds to prove your claim. With that many more out there, it should be easy for you to find some.

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  7. Why do I have to round up 76 year olds to prove what claim?

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  8. Joseph, you don't.

    But then... you knew that already.

    John's making the claims, so it's for him to prove. And he can't.

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  9. David, My claim is that you can't find any 76 year olds because they don't exist. Your claim that there is no epidemic and the numbers have been the same since the dawn of creation leaves it up to you to find some of those old folks with autism.

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  10. No, Johh - no. I should know better, but let me try to explain. You just made a claim. That we (meaning "no one") can't possibly find any autistic 76 year olds. That's an extraordinary claim and an easy claim to refute actually. But let's say you claimed that no one could possibly find autistic 76 year olds at a 1% rate. What is the evidence of this claim? Are you aware of an epidemiological study of 76 year olds by chance?

    Clearly you have no evidence to support your claim, period.

    As to the claim that there's no epidemic, we could debate who's got the burden of proof on that one. But either way, it's not necessary to find 76 year olds to disprove it. It's only necessary to do a screening of many birth year cohorts within the last couple of decades (that's one way). This sort of thing has been done, finding a high but stable prevalence.

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  11. Liz here from I Speak of Dreams.

    A note of clarification. The term "learning disability" means different things in North American and elsewhere in the English-speaking world.

    from Wing and Potter:

    Because we concentrated on the children with learning disabilities (IQ under 70)

    That's the non-North American definition of "learning disabilities", meaning IQ under 70. In North America, those with IQs under 70 are referred to formerly as "mentally retarded" and latterly as "developmentally delayed."

    In the US, "learning disabilities" refer to

    National Institute of Neurological Disorders and Stroke

    What are Learning Disabilities?
    Learning disabilities are disorders that affect the ability to understand or use spoken or written language, do mathematical calculations, coordinate movements, or direct attention


    Previously, it was assumed that one hallmark of LDs was that there was a discrepancy between the individual's capacity to learn (as represented by IQ being at least 70) and the individual's performance.

    It's hard to quantify, but I've noticed a change in the last few years -- in other words, a person may have an IQ below 70 and have disorders of learning.

    And of course, there's the whole question of IQ-testing validity for those with significant communication delays.

    Joseph, have you seen the book and website "The Mislabeled Child" ?

    http://mislabeledchild.com/

    the Eides' blog

    Eide Neurolearning

    here's their take on the study

    CDC 1-150 Incidence for Autism

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  12. Thanks Liz.

    Yeah, in IDEA there's "Specific Learning Disability" which is separate from mental retardation and I understand its diagnostic criteria is fairly ambiguous. The common definition of SLD is the following:

    "A specific learning disability shows itself in the child's ability to listen, think, speak, read, write, or to do mathematical problems."

    Incidentally, there has been a substantial reduction in the prevalence of SLD as that of autism has increased - at least in California I've noticed that's the case.

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  13. I wonder if there's a Canadian definition..... I never considered Alex to be "learning disabled" and never heard him referred to as such, even though he started grade 1 with a 3 word vocabulary.

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  14. The irony is that there can never be a number any more than we will see an end to Pi, because autism is an ever moving social construction, a human mirror of something that cannot be weighed numbered and divided.

    I can see this, why I wonder cannot anyone else.

    It is a paradox, as sure as the problem of how Bernard Matthews English Turkeys got Bird Flu from the Hungarian ones, perhaps it was quantum transmission of the virus ?

    It all comes back to the ship of Theseus doesn't it, or how long is the British coastline.

    You have to be sure that autism is as discrete an entity as a two headed frog, but alas for the statistical idiots it is not.

    Putting it another way, if the autistic brain were an engine, when is a diesel when a petrol engine is running on?

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  15. The irony is that there can never be a number any more than we will see an end to Pi, because autism is an ever moving social construction, a human mirror of something that cannot be weighed numbered and divided.

    I can see this, why I wonder cannot anyone else.

    It is a question of when is a diesel when a petrol engine is running on, a question of moving targets and uncertain definitions

    What is a Jaffa cake, biscuit or cake, that is for lawyers to decide.

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  16. The Irony is

    When is a post what one thought it was when e blogger continues to cock up?

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  17. John Best with his ifefutable logic states that no 76 year olds exist.

    What does everybody die at 75 then?

    He failed to mention whether he was talking of autistics, or the general population, however if mercury poisoning were autism, is there an age limit on that too or was mercury non existant as an element before 1930?

    by the same logic, before the curies discovered radium, did it exist at all?

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  18. Joseph, To prove your point, you can screen any decades you want after 1931. You'll find mercury poisoning misdiagnosed as autism. If you screen any decades you want prior to 1931, you will only find a few cases of fragile X and some mad hatters.
    Nobody would do a study for a condition that did not exist so there would be no point in studying those over 76 years of age. Kanner would have known of their existence if they existed.
    BTW, did you know that I cured my younger son of ADD by removing mercury from his brain? That proves that mercury causes ADD. So, while you're looking for 76 year old autistics, why don't you see if you can find some old folks with ADD too?

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  19. Larry, Nobody was poisoning people with mercury in vaccines until 1931. That's why you're autistic.

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  20. John: "Larry, Nobody was poisoning people with mercury in vaccines until 1931. That's why you're autistic."

    Way off base, John.

    You've already been told probably a thousand times why your statement is just so wrong.

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  21. John: "BTW, did you know that I cured my younger son of ADD by removing mercury from his brain? That proves that mercury causes ADD."

    You haven't actually proven that, John. You just say that it's so. Without a proper study (accounting for confounding variables, and methodology and so on) you can't say that you've proven anything.

    You can say that you believe that the ADD in one son and the autism in Sam is caused by mercury, but without something more conclusive, you have not actually proven anything.

    Now, trying to keep things on topic here:

    The first prevalence figure I was aware of in my own studies about autism was the NAS figure of 91/10000 (essentially the ~1% figure), and that was back in 1996.

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  22. BTW, did you know that I cured my younger son of ADD by removing mercury from his brain?

    I heard that you determined that your son's grades improved suddenly in a couple months. I've been in school John. I don't see how you did that. I also don't see why you equate ADHD with school grades.

    And gambling is a good way to make money in your view, right?

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  23. Joseph, Gambling is a great way to make money! Just ask anyone who made a fortune in the stock market. The ROI in playing horses can be much better. It's also more rewarding intellectually. And, you don't have to pay broker fees to cash in your winnings or pay penalties for short term profits.

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  24. This is off-topic, but there's a big difference between the stock market and the ponies. In the stock market, if there's a general upward trend in the average stock price, the average investor will always be making money. Gambling, on the other hand, is a business designed such that gamblers, on the whole, will lose money over time. And that's how it works in practice, of course. Presumably some sports gamblers have enough expertise to improve their odds, but it's always an uphill battle against the expertise of those who set the betting odds.

    It's a similar situation with those who think that if they buy enough lottery tickets over time, they will eventually win the lottery. In average, however, more money will be spent in lottery tickets than whatever money is won.

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  25. Joe, Nobody sets odds on horse races which is why it's much different than betting on other sports, casino games or lotteries. The odds are determined by the public. In the races I won today, the winning odds were 10 to 1 and 16 to 1. I missed a race because my son's aide didn't show up for work and that horse that I would have played was 23 to 1. I only played 7 races all day. So, you can see that I only needed one winner to make money for the day. I'm surprised more autistic people who love to analyze statistics don't become involved in horse racing. Instead of trying to "spin" statistics to make it look like there is no autism epidemic, you could be analyzing horses and result charts and make yourself a fortune.

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  26. As the autism prevalence approaches 1% (or, in fact, has exceeded it), a few questions come to mind:

    [1] Has the diagnosis of "autism" become so broad and all-inclusive that it has lost all utility?

    After all, the real reasons for making a diagnosis are (a) to apply the correct treatment (when available), (b) to give the patient and/or their family some idea of what to expect in the future (prognosis). As I see it, the diagnosis of "autism" has not served either function for several decades.

    There is no treatment or group of treatments that have been show to be effective. And the extreme breadth of the "autism" diagnosis may be contributing to that lack. By lumping together people who most likely have very different disorders (if they have a "disorder" at all), it becomes problematic (a nice word for impossible) to find a treatment that works for any one sub-group.

    This both frustrates the researchers who are trying to find real treatments for autism and provides protective cover for people providing pseudo-therapies. If a diagnosis of "autism" could be expected to encompass one or a small number of disorders, it would be easier to find effective therapies and easier to spot those "therapies" that clearly don't work.

    [2] Is there any hope that the proponents of the mercury-causes-autism hypothesis will ever admit that the very phenomenon that "caused" the "autism epidemic" (i.e. greater awareness coupled with looser/broader diagnosis) is what is forcing them to resort to extreme measures (e.g. the "Chinese mercury emissions" story) to keep their hypothesis alive?

    A few mercury-autism proponents have take a few shaky steps in that direction, "explaining" that changes in diagnosis have prevented the world from seeing how removing thimerosal has impacted autism rates. They fail to see how attacking the current data undercuts their entire position.

    Of course, most of the more vocal proponents have adopted an "activism means never having to say you're sorry" (or wrong) attitude and are currently tilting at Chinese mercury, power plants and homeopathic levels of thimerosal in vaccines. Those who wish to keep their focus on vaccines (for whatever reason) have championed a switch to aluminium, formaldehyde or other mysterious vaccine components.

    It looks as though the thimerosal ship is coming apart at the seams and we all have a ringside seat.

    Popcorn, anyone?


    Prometheus

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  27. David, In the US, the odds are determined by how much is bet on each horse. Most bookies here won't take bets on horses. When they do, they won't pay more than 30 to 1.

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  28. Okay, John; point taken. In the UK, the bookies set them, based on the money taken on particular horses; public bets, but the bookies calculate the odds and set the prices.

    I have to take your word on the US practice if it's a slightly different situation (which, let's face it, it could be).

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  29. Prometheus: You're probably right that autism is not a very good medical definition, but I'd add that's the case however broad or narrow it's made. Prognosis is unpredictable. There's not a whole lot in the way of proven treatments. Even some treatments that are generally considered evidence based and mainstream don't have a randomized trial showing their effectiveness. (However, I would recommend checking out the work of Dr. Gernsbacher for some approaches that seem both ethical and effective).

    That's why I tend to agree with Larry to an extent. Autism is best understood as a cultural construct. And this nicely explains such phenomena as the "autism epidemic".

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  30. For John Best Jr: "By adjusting the odds in his favour or by having a point spread, the bookmaker will aim to guarantee a profit by achieving a 'balanced book', either by getting an equal number of bets for each outcome, or (when he is offering odds) by getting the amounts wagered on each outcome to reflect the odds."

    This (I should add) reflects UK practice.

    Joseph: "Autism is best understood as a cultural construct."

    Yes. A cultural construct about differences in social development, which is one reason why I feel that it is best left to educational psychologists rather than clinical practitioners.

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  31. Well David you would say that, being as it is pretty much socially determined that you would wish to preserve a niche for your own profession.

    I would say that medicine does not equal science and that it is very much a social practice, indeed when best practiced it needs to be social, however if the ability to practice scientific investigation were a matter of medical judgement I wonder where professor Hawking would be nowadays? and if it were left up to the worst of educational pyschologists where you and I would be?


    I do think there is a strong placebo effect implicated in parental attitudes towards the intervention they practice whether that be a hard biomedical one, an intensive one like ABA or a soft eclectic technique, and that whichever one they chose they (the parents) will not be seeing objective fact nor will they be able to seperate out just what is causing the improvement and whether it would make any difference anyway.

    I am a bit of a cynic even about educational intervention sometimes, perhaps I have listened to Pat Howlin too much, But I am currently working on coming up with an experimental protocol to test it all using the usual scientific paradigm, with the added bonus of a little post modernism phenomenology thrown in.

    The art is to test qualitative analysis by subjecting it to logical devices that would prove valid in a statistical way, and not just be an artefact of statistical manipulation which we can all do.

    In other words a rigorous method of combination of methodologies each attempting to nullify the other

    Can it be done under the Aegis of Birmingham? I dunno, but I am working on it

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  32. Larry: "Well David you would say that, being as it is pretty much socially determined that you would wish to preserve a niche for your own profession."

    To a point, sure. But certainly not to the extent that the likes of Wakefield and the Geiers are cornering a market. At least I have an ethos of not wanting to suggest more is needed than is necessary. For example, with assessments... they are needed... without doing one, it is impossible to get an idea of what difficulty is presenting and show evidence of it.

    "I would say that medicine does not equal science and that it is very much a social practice, indeed when best practiced it needs to be social,"

    yeh, to both parts of the humour thing there....

    "however if the ability to practice scientific investigation were a matter of medical judgement I wonder where professor Hawking would be nowadays?"

    That I do not know... not sure I'd want to venture there, given some of the recent medicalised evaluations of the worth of many of us...

    "and if it were left up to the worst of educational pyschologists where you and I would be?"

    Do you want the clean version or the heartfelt one?

    "Can it be done under the Aegis of Birmingham? I dunno, but I am working on it"

    Can always give it a shot....

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  33. "Incidentally, there has been a substantial reduction in the prevalence of SLD as that of autism has increased - at least in California I've noticed that's the case. "

    The drop in the number of SLD students is for ages 10-13 (mostly). The increase in students with autism is for ages<10, so there isn't evidence for substitution there.

    SLD, as I recall, is for conditions like dyslexia or other identifiable conditions.

    The age distributionof SLD kids is peaked to older students. This dovetails with the speech-delay kids who are peaked to younger kids.

    Matt

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  34. My son has child autism. My son has not been vaccinated. My son is being treated, and he is improving every day.
    Personally I do not believe that MMR causes autism, but it definitely pushes what would be borderline kids over the edge.
    I believe there is a very big case for looking at the child's inability to metabolise essential fatty acids as being a major contributory factor(either genetically caused or other).
    We just started a course of l-carnitine for our son, and his dark circles are all but gone, and he is now making great strides.
    Thanks for reading...good luck to any parents with autism in their life.

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