The data we've seen allow us to say several things with certainty.
First, autism today is not the same as autism ten or twenty years ago. The definition of autism has changed. The way autism is diagnosed has changed. Autism rates have changed dramatically. Whatever the reason, we have a new thing that we now call autism. Today's autism most likely includes what we used to call autism in the past, but it also includes a lot more than that.
This brings us to the second point - autism knowledge from the past does not always apply to today's autism. Autism has changed, and whatever we knew, or thought we knew about autism, may have changed as well.
Further, autism continues to change. While everything in nature always changes and evolves, there are things that have remained relatively stable over the years and for which knowledge accumulated over a long period of time still applies today and will most likely apply in the near future. This is not at all the case with autism. Autism is rapidly changing. This change could be simply a change of definition, or it could be a change in the biological nature of the condition. Either way, any knowledge about autism would need to account for its dynamic nature.
Finally, changes in autism have been gradual. While autism today is very different from what used to be called autism 30 years ago, it is very similar to last year's autism.
Wednesday, April 7, 2010
Monday, December 21, 2009
New Estimate of Autism Prevalence from the CDC
The CDC issued a new report presenting surveillance data from the ADDM network. The data, which was also published in this article, puts the rate of autism among 8-year-old US children born in 1998 at 0.9%. This is a significant increase over the previous report from the ADDM network, which looked at children born in 1992 and 1994. At sites which collected data both in 2002 (for children born 1994) and in 2006 (for children born 1998) there was a 57% increase in prevalence during this period.
Tuesday, June 2, 2009
More Data from California
The California Department of Developmental Services has more data available on their website. These include monthly caseload data, and comparing those to the autism caseload and to the total population of California might provide some interesting insights. For example, we may note that the total caseload of DDS as of April 2009 is 202,924. This compares to a total California population of approximately 38 million, so about 1 in 187 Californians currently receive DDS services. In December 2001 the DDS caseload was 154,862 and the population of California was about 35 million. Thus about 1 in 226 Californians received DDS services in 2001.
Monday, May 18, 2009
California Data
One of the main reasons why many people believe there has been a significant increase in autism are the data of the California Department of Developmental Services. A document worth examining in this context is the report on changes in the California caseload.
Friday, May 1, 2009
Agreements and Disagreements
Reviewing the literature, there are several facts that everyone seems to agree on. Diagnoses of autism have steadily increased since the early 1990's. The definition of autism is now broader than it was in the early 1990's. Autism awareness has significantly increased during this period.
There is no agreement on the reasons for these changes. Let's review some recent research.
Hertz-Picciotto I, Delwiche L. The Rise in Autism and the Role of Age at Diagnosis. Epidemiology. 20(1):84-90, January 2009
Using data from California, the authors argue that "younger ages at diagnosis, differential migration, changes in diagnostic criteria, and inclusion of milder cases do not fully explain the observed increases." The autors attempt to calculate the increse that is likely explained by each of the above factors, concluding that the total of all these factors would be insufficient to explain the overall rise in diagnosed autism.
Morton Ann Gernsbacher, Michelle Dawson, and H. Hill Goldsmith, Three Reasons Not to Believe in an Autism Epidemic; Current Directions in Psychological Science. 2005 14(2)
The autors list a number of factors that have contributed to the autism diagnosis increase. They do not attempt to quantify the contribution of each factor.
Bishop DV, Whitehouse AJ, Watt HJ, Line EA. Autism and diagnostic substitution: evidence from a study of adults with a history of developmental language disorder. Dev Med Child Neurol. 2008 Mar 31
The autors provide evidence for diagnostic substitution by examining a sample of 38 adults with a history of developmental language disorder. They conclude that 12 of these patients would "nowadays be diagnosed unambiguously with autistic disorder."
Paul T. Shattuck. The Contribution of Diagnostic Substitution to the Growing Administrative Prevalence of Autism in US Special Education. PEDIATRICS Vol. 117 No. 4 April 2006, pp. 1028-1037
The author presents evidence of diagnostic substitution in special education data. He further argues that "prevalence findings from special education data do not support the claim of an autism epidemic because the administrative prevalence figures for most states are well below epidemiological estimates."
More articles to review...
Chakrabarti S, Fombonne E. Pervasive developmental disorders in preschool children: confirmation of high prevalence. Am J Psychiatry. 2005 Jun;162(6):1133-41.
Fombonne E. Epidemiology of autistic disorder and other pervasive developmental disorders. J Clin Psychiatry. 2005;66 Suppl 10:3-8.Click here to read
Jick H, Kaye JA. Epidemiology and possible causes of autism. Pharmacotherapy. 2003 Dec;23(12):1524-30.
Rutter M. Incidence of autism spectrum disorders: changes over time and their meaning. Acta Paediatr. 2005 Jan;94(1):2-15.Click here to read
Taylor B. Vaccines and the changing epidemiology of autism. Child Care Health Dev. 2006 Sep;32(5):511-9.
There is no agreement on the reasons for these changes. Let's review some recent research.
Hertz-Picciotto I, Delwiche L. The Rise in Autism and the Role of Age at Diagnosis. Epidemiology. 20(1):84-90, January 2009
Using data from California, the authors argue that "younger ages at diagnosis, differential migration, changes in diagnostic criteria, and inclusion of milder cases do not fully explain the observed increases." The autors attempt to calculate the increse that is likely explained by each of the above factors, concluding that the total of all these factors would be insufficient to explain the overall rise in diagnosed autism.
Morton Ann Gernsbacher, Michelle Dawson, and H. Hill Goldsmith, Three Reasons Not to Believe in an Autism Epidemic; Current Directions in Psychological Science. 2005 14(2)
The autors list a number of factors that have contributed to the autism diagnosis increase. They do not attempt to quantify the contribution of each factor.
Bishop DV, Whitehouse AJ, Watt HJ, Line EA. Autism and diagnostic substitution: evidence from a study of adults with a history of developmental language disorder. Dev Med Child Neurol. 2008 Mar 31
The autors provide evidence for diagnostic substitution by examining a sample of 38 adults with a history of developmental language disorder. They conclude that 12 of these patients would "nowadays be diagnosed unambiguously with autistic disorder."
Paul T. Shattuck. The Contribution of Diagnostic Substitution to the Growing Administrative Prevalence of Autism in US Special Education. PEDIATRICS Vol. 117 No. 4 April 2006, pp. 1028-1037
The author presents evidence of diagnostic substitution in special education data. He further argues that "prevalence findings from special education data do not support the claim of an autism epidemic because the administrative prevalence figures for most states are well below epidemiological estimates."
More articles to review...
Chakrabarti S, Fombonne E. Pervasive developmental disorders in preschool children: confirmation of high prevalence. Am J Psychiatry. 2005 Jun;162(6):1133-41.
Fombonne E. Epidemiology of autistic disorder and other pervasive developmental disorders. J Clin Psychiatry. 2005;66 Suppl 10:3-8.Click here to read
Jick H, Kaye JA. Epidemiology and possible causes of autism. Pharmacotherapy. 2003 Dec;23(12):1524-30.
Rutter M. Incidence of autism spectrum disorders: changes over time and their meaning. Acta Paediatr. 2005 Jan;94(1):2-15.Click here to read
Taylor B. Vaccines and the changing epidemiology of autism. Child Care Health Dev. 2006 Sep;32(5):511-9.
Monday, November 17, 2008
Why No Increase?
With such clear data, why would anyone think there is no increase in autism?
Critic of the "autism epidemic" point of view centers around several issues. At the basis of these issues lies diagnosis substitution. An autistic person would not have been diagnosed with autism in the 17th century because Kanner first described autism in 1943. If there were autistic people prior to 1943 they would have been diagnosed differently. Most likely they would be considered developmentally delayed or mentally retarded. Maybe Kanner just described as a separate condition what was earlier considered a subset of mental retardation and/or developmental delays. As his definition became better known and accepted by other physicians and psychiatrists an increasing number of people were diagnosed as autistic.
Diagnosis substitution has been driven to a large degree by broadening of diagnostic criteria. Over the years there have been several revisions of the autism definition, each time broadening the criteria to include more cases. One could actually view Kanner's paper as the first broadening of the autism definition. Every time the autism definition is expanded diagnosis substitution increases.
Another frequently raised point is that in recent years the societal stigma of having autism has been significantly reduced and many services have been offered to autistic individuals. This has provided incentives for doctors to give autism diagnosis to their patients, thus making them eligible for services. Again, this results in wider diagnosis substitution.
Besides diagnosis substritution, it is possible that, as criteria and awareness of autism have expanded, many high-functioning autistics who would not have been diagnosed with any disability in times past are now receiving an autism diagnosis.
All these trends are undeniable. But are the effects sufficient to fully explain the increase in autism diagnosis? This issue is controversial and very important. If there is an actual significant increase in autism, then there is likely an environmental cause. Research efforts should be focused on finding this cause or causes. A significant increase in recent years would point to some assault that has been introduced and/or significantly increased recently, such as pesticides, immunizations, environmental polution, etc. If, on the other hand, there isn't a real increase in autism there would be little reason to focus significant research efforts on recent environmental changes.
With this in mind, it is well worth it to examine the available studies on autism prevalence.
Critic of the "autism epidemic" point of view centers around several issues. At the basis of these issues lies diagnosis substitution. An autistic person would not have been diagnosed with autism in the 17th century because Kanner first described autism in 1943. If there were autistic people prior to 1943 they would have been diagnosed differently. Most likely they would be considered developmentally delayed or mentally retarded. Maybe Kanner just described as a separate condition what was earlier considered a subset of mental retardation and/or developmental delays. As his definition became better known and accepted by other physicians and psychiatrists an increasing number of people were diagnosed as autistic.
Diagnosis substitution has been driven to a large degree by broadening of diagnostic criteria. Over the years there have been several revisions of the autism definition, each time broadening the criteria to include more cases. One could actually view Kanner's paper as the first broadening of the autism definition. Every time the autism definition is expanded diagnosis substitution increases.
Another frequently raised point is that in recent years the societal stigma of having autism has been significantly reduced and many services have been offered to autistic individuals. This has provided incentives for doctors to give autism diagnosis to their patients, thus making them eligible for services. Again, this results in wider diagnosis substitution.
Besides diagnosis substritution, it is possible that, as criteria and awareness of autism have expanded, many high-functioning autistics who would not have been diagnosed with any disability in times past are now receiving an autism diagnosis.
All these trends are undeniable. But are the effects sufficient to fully explain the increase in autism diagnosis? This issue is controversial and very important. If there is an actual significant increase in autism, then there is likely an environmental cause. Research efforts should be focused on finding this cause or causes. A significant increase in recent years would point to some assault that has been introduced and/or significantly increased recently, such as pesticides, immunizations, environmental polution, etc. If, on the other hand, there isn't a real increase in autism there would be little reason to focus significant research efforts on recent environmental changes.
With this in mind, it is well worth it to examine the available studies on autism prevalence.
Monday, October 27, 2008
Why an Increase?
Why would anybody think there might be an increase in autism?
When autism was first described by Dr. Kanner, he said that this is an extremely rare disorder. At the time autism prevalence was estimated at about 1 in 10,000. The most recent CDC estimates are about 1 in 150. If the word 'autism' still retains its original meaning and these estimates are even remotely accurate than there is a huge increse in autism. Moreover, there have been a number estimates inbetween those two and one may notice that estimates of autism prevalence have steadily increased over time.
Also, the number of children enrolled in special education in California with a diagnosis of autism has been on a steady increase over the last 17 years, ever since 'autism' was introduced as a separate cathegory by the Department of Developmental Services in 1991.
When autism was first described by Dr. Kanner, he said that this is an extremely rare disorder. At the time autism prevalence was estimated at about 1 in 10,000. The most recent CDC estimates are about 1 in 150. If the word 'autism' still retains its original meaning and these estimates are even remotely accurate than there is a huge increse in autism. Moreover, there have been a number estimates inbetween those two and one may notice that estimates of autism prevalence have steadily increased over time.
Also, the number of children enrolled in special education in California with a diagnosis of autism has been on a steady increase over the last 17 years, ever since 'autism' was introduced as a separate cathegory by the Department of Developmental Services in 1991.
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