Thursday, May 17, 2012

Study : Global Prevalence of Autism and Other Pervasive Developmental Disorders.

I am constantly amazed that otherwise rational people can look at the steady upward march of autism prevalence numbers and confidently state that it isn't real.  Certain researchers seem to always pull out the better awareness, broadening criteria, diagnostic substitution, and availability of services arguments to explain away any increases without ever taking the time to empirically demonstrate that these factors are actually responsible for the increase.

It might be just me, but if you are going to put forth a theory then you had best have evidence to support that that theory.  Otherwise your theories are just speculation and are no better than all of the other unsupported ideas surrounding autism, such as the extreme male brain theory of autism.

I haven't read the full text of this recent paper on global prevalence (abstract below), but from the abstract it seems to yet another "the sky isn't falling, we are just better at seeing it" type of paper.  Which, in light of all the recent research into autism prevalence and causes, just seems badly out of touch.

I have to wonder at what point the epidemic denialists will stop pulling out the same tired reasons to keep explain away the ever increasing number of people with autism.  As worldwide autism rates go from well under 1% to Korea style over 2% and beyond, at exactly what point will the denialists stop using the exact same theories to explain each and every increase?  How many times can the spectrum double before these reasons start to sound just like excuses?

Are we really going to have to wait for the sky to finish falling and literally hit them in the face before they will admit that there is in fact a problem?

Global Prevalence of Autism and Other Pervasive Developmental Disorders.

Elsabbagh M, Divan G, Koh YJ, Kim YS, Kauchali S, MarcĂ­n C, Montiel-Nava C, Patel V, Paula CS, Wang C, Yasamy MT, Fombonne E.

We provide a systematic review of epidemiological surveys of autistic disorder and pervasive developmental disorders (PDDs) worldwide. A secondary aim was to consider the possible impact of geographic, cultural/ethnic, and socioeconomic factors on prevalence estimates and on clinical presentation of PDD. Based on the evidence reviewed, the median of prevalence estimates of autism spectrum disorders was 62/10,000. While existing estimates are variable, the evidence reviewed does not support differences in PDD prevalence by geographic region nor of a strong impact of ethnic/cultural or socioeconomic factors. However, power to detect such effects is seriously limited in existing data sets, particularly in low-income countries. While it is clear that prevalence estimates have increased over time and these vary in different neighboring and distant regions, these findings most likely represent broadening of the diagnostic concets, diagnostic switching from other developmental disabilities to PDD, service availability, and awareness of autistic spectrum disorders in both the lay and professional public. The lack of evidence from the majority of the world's population suggests a critical need for further research and capacity building in low- and middle-income countries. Autism Res 2012

PMID: 22495912 DOI: 10.1002/aur.239


  1. I wonder but I don't know. This image makes me suspicious that it is monetary. My son was diagnosed with PDD at age 3. Had I known how far he would come I would not have worried myself sick.

    It's like a gravy train in the US. That does not diminish the seriousness of it. We are so good at diagnosis, if we were only so good at helping.

    1. Hmmm, I'm not so sure it is about the money.

      I have yet to run across a child with a label of autism who didn't meet the criteria for autism. Or at least a child with a label of autism where the parents were involved at it wasn't the child announcing for themselves that they have autism. If anything, the parents I know are reluctant to accept the autism label and fight against accepting it.

      At least in my area, the people who make the diagnosis of autism and the people who could potentially profit from it are two very different groups.


    So, increased (fashionable) diagnosis definitely happens.

    1. Anonymous,

      Yes, diagnostic substitution does happen.

      But no one - including the post you have referenced - can actually demonstrate that that factor alone, or combined with the other typical reasons, can account for the majority of the increase in the cases of autism.

      The best yet still very much pie in the sky estimate to date (Bearman) suggests that only half of the increase might be explainable by increased awareness, diagnostic substitution, and better services. But even this estimate is flawed in many ways which probably means that it too is wrong.

      On another note, it is always worth the time to look at what studies a person is using to support their position to see if it actually does.

      For example, the Brugha study of adults with autism didn't actually find that the rates "didn't change with age". What they actually said was that there wasn't even data but when grouped into buckets of 30 years, there was a gentle downward slope. But that was based on about 19 actual cases of autism in a population of thousands.

      Whats more, the screening tool that they study authors invented for that particular study, the AQ-20 was later found to be a poor test for autism. So the estimates made in that study are unreliable.