Several weeks ago I argued that much of the the observed increase in autistic disorder over time can be explained by three phenomenon: (1) Diagnostic criteria have changed over some part of the period during which increases have been observed. The diagnostic criteria for autistic disorder were broadened over time. (2) The average age of diagnosis for autistic disorder became younger. (3) The efficiency of ascertainment (the probability that a true case is identified) has increased with greater awareness of the condition, introduction of new treatments and new resources, advocacy, broadening of diagnostic experience, and changes in diagnostic practices.

In another post in May I described a small study from England that “adds to arguments against the view that incidence of autism has increased over recent decades, and suggests that changes in diagnostic criteria are the most likely reason for the rise in the number of cases diagnosed.” I pointed out, however, that this small study was only a first step and we need more studies with larger sample sizes.

In the July 2008 issue of the the Journal of Autism and Developmental Disorders a much larger and more elegant study has been published. I would love to give you a detailed description, but I’m about to go on vacation. So quoting the abstract will have to suffice for now.

Trends in Autism Prevalence: Diagnostic Substitution Revisited

By Helen Coo and Hélène Ouellette-Kuntz of the Department of Community Health and Epidemiology, Queens University; Jennifer E. V. Lloyd of the Human Early Learning Partnership (HELP); and three other authors.

SUMMARY: The authors examined trends in assignment of special education codes to British Columbia (BC) school children who had an autism code in at least 1 year between 1996 and 2004, inclusive. The proportion of children with an autism code increased from 12.3/10,000 in 1996 to 43.1/10,000 in 2004; 51.9% of this increase was attributable to children switching from another special education classification to autism (16.0/10,000). Taking into account the reverse situation (children with an autism code switching to another special education category (5.9/10.000)), diagnostic substitution accounted for at least one-third of the increase in autism prevalence over the study period.

Sphere: Related Content

10 Responses to “Trends in Autism Prevalence: Diagnostic Substitution Revisited”  

  1. 1 john

    Key realities about autism, vaccines, vaccine-injury compensation, Thimerosal, and autism-related research

  2. 2 andrea

    Not only have diagnostic criteria changed over the years, but so has bureaucratic reporting.

    Schools did not used to have services for autistic children; now they do. To get services, children would have received them (if they did) under other labels.

    Schools did not offer as many services before Section 504 of the ADA (Americans with Disabilities Act) was passed in 1973. So naturally, parents did not ask for services that did not exist! There are a lot of bureaucrats who will assume that, “if people aren’t asking, then there is no need”.

    Schools were formerly not required to track how many autistic children they served with special services; now they do. We all know that no one is going to keep track of information unless they have to! Lack of records does not indicate lack of autistic children — it just means lack of records.

    “Absence of data is not the same thing as data of absence.”

    Thank you so kindly for posting the new study!


  3. 3 EpiWonk
  4. 4 RAJ

    There was another rise in the incidence of autism that occured within a decade of Kanner’s paper published in 1943 that defined ‘autism’. In 1965 Kanner explained the phenomena which had disappeard by the mid 1960’s. Kanner explained this long forgotten autism ‘pandemic’ as one not of broading diagnostic criteria but one of gross misdiagnosis. His explanation is relevant to the current disussion of the myth of a global autism pandemic.

    Kanner wrote :
    “Moreover, it became a habit to dilute the original concept of infantile autism by diagnosing it in many disparate conditions which show one or another isolated symptom found as a part feature of the overall syndrome. Almost overnight, the country seemed to be populated by a multitude of autistic children, and somehow this trend became noticeable overseas as well”.

    The trend to misdiagnosis of autism can be traced to various editions of the APA’s DSM’s starting in 1980:

    In DSM-III (1980) Kanner’s definition ‘Pervasive lack of responsiveness to other people (autism)’ was required to qualify for an ‘Autism Spectrum Disorder’.

    In the revised DSM-III-R (1987) Kanner’s definition was relegated to just one of five isolated symptoms in the social domain and was not required to qualify for an ASD diagnosis. A field trial comparing DSM-III to DSM-III-R criteria found that ‘autism was being overdiagnosed:

    When DSM-IV (1994) was introduced, the subsequent years produced an astounding seemingly worldwide autism pandemic with prevelance rates sky rocketing from 4 to 6 cases per 10000 to 1 per 150. DSM-IV completly removed Kanner’s definition and replaced it with the vague, ambigous and subjective:

    ‘Qualitative impairment in social interaction’

    This has resulted in conferring an ASD diagnosis in children who would never have qualified for an ‘autism’ diagnosis using Kanner’s defnition in DSM editions prior to 1987, including mentally retarded children with ‘autistic-type’ behaviors and Romanian orphans subjected to extreme social isolation and were adopted into well-functioning English families who also meet diagnostic criteria for an ASD. We now have the same phenoma of what Kanner described in 1965:

    “Almost overnight, the country seemed to be populated by a multitude of autistic children”

    What would Kanner have called the APA’s committee on Autism and the PDD’s who were responsible for the diagnostic criteria published in DSM-IV in 1994? More than likely he would have described the framers of DSM-IV as ‘acrobatic jumpers who go in for the summary adoption of diagnostic cliches and have found a new bandwagon, ‘Autism Spectrum Disorders”. Had the framers of DSM-IV used a more accurate and descriptive label such as neurodevelopmental disorder spectrum and reserved Kanner’s definition for the small subgroup who actually met diagnostic criteria for Kanner’s definition, the entire myth of a global autism pandemic could have been avoided.

  5. 5 Uncle Dave

    Epe Wonk wrote;
    “I pointed out, however, that this small study was only a first step and we need more
    studies with larger sample sizes.”

    My spouse who has been in special education for approimately 30 years now seems to hold a
    different opinion on this matter. She would argue based on her own experience throughout
    the years that autism or prevalance of autism has increased. She sees more children
    today then she did before with an accurate autism label. This is by no means a irrefutable
    evidence, however in her small study group (her experience in a southern california region for
    the last 20 years)she has noticed an increase in the amount of children identified as Autistic.

    This could be a regional issue where she happens to teach, but non the less she
    sees more children with autism traits today then ever before. This observation has nothing to do
    with changes in diganostic criteria or official reporting methods being adopted.

    The possibility of “gross misdiagnosis” is a valid issue globally as RAJ stated.

    Keep in mind that this personal observation makes no conclusion as to reason or cause, just that
    there does seem to be a greater prevalance today then say 10-15 years prior.

    Reporting issues (by parent or foster parent) have a great deal to do the misunderstanding
    origins and family history. Many foster parents are more than willing to identify the foster child
    in thier care as a drug baby or that mom or dad where drug addicts etc. etc. This sometimes
    is due to the fact that subsidy of the foster care for the child is regulated by degree of disability
    (the worse they are the more money they get).
    Many biological parents tend to be a bit more closer to the hip as to information
    about any circumstances such as pre-term and drug usages prior to birth for obvious reasons.

    These studies require a lot of investigation as to source of the information obtained.
    I have not read some of the studies here yet but there seems to be a real issue still
    unresolved as to a more reliable measure of incidence.

  6. 6 Joseph

    I’ve done the following analysis with IDEA data. For 6-11 year olds I got second-order polynomial fits of prevalence trends for autism and mental retardation between 1993 and 2006. I got the residuals of these trends and put them in a scatter. The slope of the scatter was -2.73 with 95% CI -7.123 to 1.672. So it’s in the expected direction, but I didn’t get statistical significance. That’s why I haven’t written about it. With more data points, I expect it can be shown that the downward trend of MR and upward trend of autism are not coincidental.

  7. 7 RAJ

    Here is another of Kanner’s spot on observation’s related to a long forgotten autism pandemic. In the 1990’s The subject of Romanian orphans who were placed in institutions shortly after birth has been the subject of autism researcher interest. The orphans were placed in horrendous institutions and suffered from extreme emotional deprivation. A subgoup of these orphans met diagnostic criteria for an Autism Spectrum Disorder (DSM-IV). A recent followup study has given these orphans a new label ‘Pseudo-autism’.

    Kanner in 1965 also noticed this trend for defining some children using the diagnostic cliche ‘Pseudo-autism’. He wrote in 1965:

    “To complicate things further, Crewel, in the hope of avoiding confusion between true autism and other conditions with autistic-like features, suggested the term pseudo-autism for the latter. Even this term came to be employed haphazardly, and conditions variously described as hospitalism, anaclitic depression, and separation anxiety were put under the heading of pseudo-autism”

  8. 8 RAJ


    You made the following observation regarding the issues of diagnostic criteria:

    “(1) Diagnostic criteria have changed over some part of the period during which increases have been observed. The diagnostic criteria for autistic disorder were broadened over time”.

    Broadening of diagnostic criteria has been invoked to explain the appearance of a global autism pandemic. ‘Broadening’ implies a base where autism is narrowly defined and broadening the criteria will be more inclusive for the larger group of children who were in trouble developmentally but defied categorization. In fact, ‘broadening of diagnostic criteria’ is linguistic acrobatics. The narrow definition of ‘autism’ was not broadened, it was completly abandoned in 1994 with the removal of Kanner’s criteria.

  9. 9 mild autism signs symptoms checklist

    Hello. This is kind of an “unconventional” question , but have other visitors asked you how get the menu bar to look like you’ve got it? I also have a blog and am really looking to alter around the theme, however am scared to death to mess with it for fear of the search engines punishing me. I am very new to all of this …so i am just not positive exactly how to try to to it all yet. I’ll just keep working on it one day at a time Thanks for any help you can offer here

  10. 10 five mistakes

    Your site is really interesting to me and your subject matter is very relevant. I was browsing around and came across something you might find interesting. I was guilty of 3 of them with my sites. “99% of site managers are doing these five mistakes”. You will be suprised how easy they are to fix.

Leave a Reply