1 In 166. Really?

In a recent blog post, David Kirby repeated the oft-cited figure of 1 in 166 people now having autism. That figure, according to Kirby, used to be 1 in 5000 in the eighties.

He goes on to ask that if autism is solely genetic then where are all the old autistics now?

As a writer, Kirby is pretty good. As a researcher he’s suspect and prone to errors. As a critical thinker he’s woeful.

Something happened between now and the eighties alright. Something that can definitely account for the increase in prevelance. Simply put – the criteria changed. What constituted autism changed between the eighties and now. Changed drastically. Changed so much in fact that a lot of diagnosticians doubt that Hans Asperger would recognise what is now considered to define Aspergers Syndrome, changed so much that people who were once thought of as AS would be today diagnosed as autistic.

The diagnostic criteria in the DSM, which provide a differentiation between autism and Asperger’s syndrome, have been examined by several research studies over the last five years. There has been some criticism from clinicians and research that the criteria do not identify the disorder Hans Asperger originally described. The four cases he described in his original paper would be diagnosed, according to DSM criteria, as having autism not Asperger’s syndrome. (Miller and Ozonoff 1997).

Dr Tony Attwood

So here we are with this sudden reclassification of a lot of peoples diagnosis. Further, those who would one have been classed as having Aspergers are now routinely being diagnosed as being autistic. I don’t have any stats (and I doubt they exist) on these numbers but common sense would indicate that these people make a real and significant (and continuing) impact on prevelance rates.

Going back one stage for a moment – who exactly is Kirby referring to with this ‘1 in 166’ figure? Is he talking about the prevelance of ASD? Or is he talking about the prevelance of Kanners (classical) autism? You see, the words ‘autism’ and ‘ASD’ are, in modern medical history, interchangeable. I don’t know but my gut feeling is that when people quote this 1 in 166 number they are referring to ASD – the spectrum of autism and not Kanners autism in particular.

If I’m right then we have another huge amount of people to add to our prevelance rates – the recently diagnosed. As stated the diagnostic criteria has significantly widened and as it has, the number of medical and non-medical people trained to spot ASD’s has risen massively. It doesn’t take a genius to figure out what would happen if you vastly widened the qualifying criteria for something and vastly increased the opportunity to see if people did qualify.

There are people (I know some of them) who in their thirties suddenly discover that the problems they’ve managed to live with since childhood actually have a name and an overridding condition. These people get diagnosed too.

Why is it that I know about these people and the likes of Kirby and the various mercury zealots do not (or choose not to?). Because I talk to autistic people. I don’t talk to their parents, or their carers or their advocates. I talk to them. I hear their stories and it all comes out – some (most) were diagnosed in childhood but a significant (and growing) number are getting their diagnosis’ as adults. They can do this because more is known about autism and their are more places to go and ask. When you couple this with the widening of the diagnostic criteria then you suddenly include a whole range of middle aged people who weren’t able to be included in ‘official’ stats before.

So can these people account for all of the ‘1 in 166’. I have no idea. But then I also have no idea who Kirby et al are actually counting when they reach these figures. Kanners autistics? Those with Aspgers Syndrome? Those with a generalised Pervasive Developmental Disorder? Tourettes? In the eighties it was Kanners. Today, autism is all of the above.

Variation in the administrative prevalence of ASD is associated with education-related spending, which may be associated with better-trained educational staff who can recognize the problem, and more and better trained in-school specialists who can provide screening. It is also associated with the availability of health care resources. Increased access to pediatricians and school-based health centers may lead to improved recognition of ASD. Interstate variability in the identification of ASD should be taken into account when interpreting the results of prevalence studies based on administrative data and the associated system characteristics taken into account by policy makers working to improve the recognition of ASD.

David S. Mandell, ScD; Raymond Palmer, PhD

The incidence of research-identified autism increased in Olmsted County from 1976 to 1997, with the increase occurring among young children after the introduction of broader, more precise diagnostic criteria, increased availability of services, and increased awareness of autism. Although it is possible that unidentified environmental factors have contributed to an increase in autism, the timing of the increase suggests that it may be due to improved awareness, changes in diagnostic criteria, and availability of services, leading to identification of previously unrecognized young children with autism.

William J. Barbaresi, MD; Slavica K. Katusic, MD; Robert C. Colligan, PhD; Amy L. Weaver, MS; Steven J. Jacobsen, MD, PhD

We observed dramatic increases in the prevalence of autism spectrum disorder as a primary special educational disability starting in the 1991-1992 school year, and the trends show no sign of abatement. We found no corresponding decrease in any special educational disability category to suggest diagnostic substitution as an explanation for the autism trends in Minnesota. We could not assess changes in actual disease incidence with these data, but federal and state administrative changes in policy and law favoring better identification and reporting of autism are likely contributing factors to the prevalence increases and may imply that autism spectrum disorder has been underdiagnosed in the past.

James G. Gurney, PhD; Melissa S. Fritz, MPH; Kirsten K. Ness, MPH; Phillip Sievers, MA; Craig J. Newschaffer, PhD; Elsa G. Shapiro, PhD