Understanding what "1 in 100" means for Autistic Disorder
10/11/09 15:38 Filed in: Research
There have been a number of items in the news over the past couple of weeks regarding changes in our understanding about the prevalence of autism (I was even briefly in a television interview on the subject), and these items, when taken together, begin to shape up in an interesting fashion.
Probably the most heralded item was The Center's for Disease Control (CDC) October 5, 2009 press release announcing recent research supporting a prevalence rate for Autism of 1 in 100 people, or about 1% of the general population. This rate is higher than the previously reported 1 in 150 people, of course, and at first blush continues to support the concept that autism is on the rise. However, close attention to the other information that has come out is vital when looking at the overall picture.
The study referred to by the CDC was published in the journal Pediatrics (a PDF of the article is available here - I find the Pediatrics website difficult to navigate quickly). The study used a very large sample (over 78000 participants) of children from 3 to 17 years of age. It was conducted by randomly dialing U.S. telephone numbers and conducting interviews with the parents who answered the phone. Parents were asked "if they had ever been told by a doctor or other health care provider that their child had 'autism, Asperger disorder, pervasive developmental disorder, or other autism spectrum disorder'. Parents who indicated that they had been given such a diagnosis for their child were then asked if the child currently had autism. When the parent answered "yes" to both questions the child was included in the overall total". The results from this process was that reported 110 in 10,000 respondents indicated "yes" to both questions, resulting in an extrapolated prevelance rate of right around 1 in 100, or 1% of the general population.
When we begin to look at results like this it becomes clear how important the choice of language can be to understanding these types of results. In some cases this is referred to as an "increase in the prevalence" of autism - a phrase which implies that the disorder is increasing in frequency among our population. In scientific writing, however, we are taught to be very careful with our phrasing to prevent such implications, and this is a case in point. The results of this clearly well-done and important study would be more accurately described as providing a change in our understanding about the prevalence of autism.
A study released at nearly the same time as the article in Pediatrics demonstrates this point extremely well. A study completed by the National Health Service in Great Britain looked at rates of autistic disorder among adults in that nation. That study found a prevalence rate of 1 in 100 or 1% - essentially identical to the CDC's findings for children.
The study's design is quite similar to that of the study completed by the CDC, though it uses a much smaller sample (but still over 7,000 respondents) for it's phone survey. However, in the NHS study the researchers also completed the Autism Diagnostic Observation Schedule (ADOS) - the current gold standard for autism assessment - on a subset of the respondents to further evaluate their findings. Even with evaluation using the ADOS the 1% prevalence rate held.
To my knowledge, the NHS study is the first of it's kind to investigate the prevalence of autism among adults - something we certainly must understand before we assume that the actual prevalence is rising. The results of the NHS study strongly support the idea that there are, in fact, a large number of adults in the general population with disorders in the autism spectrum. Further, those numbers are nearly identical to the numbers we are detecting in children today.
That we have not previously looked at prevalence rates among adults points to an area of concern that has been noted among professionals who work with both children and adults with developmental disabilities: Virtually all of the research in autism has been focused upon children. This is certainly understandable, as it's in childhood when we can most help.
Still, those of us who travel in both circles (child and adult treatment) have suspected for some time that there are a large number of undiagnosed adults on the spectrum in a variety of settings. I, along with several other members of the Forest City Team, have had the opportunity to work with adults in both community and institutional residential settings who clearly met the diagnostic criteria for disorders on the spectrum, but who had never been diagnosed (and in many of the cases the symptom presentation was not subtle). This is becoming thankfully less common as understanding of Autism Spectrum Disorder increases among professionals.
These studies add immensely to our understanding of what autism looks like in the general population, and, taken together, will hopefully help us understand where to most effectively focus our efforts to best assist others.
Probably the most heralded item was The Center's for Disease Control (CDC) October 5, 2009 press release announcing recent research supporting a prevalence rate for Autism of 1 in 100 people, or about 1% of the general population. This rate is higher than the previously reported 1 in 150 people, of course, and at first blush continues to support the concept that autism is on the rise. However, close attention to the other information that has come out is vital when looking at the overall picture.
The study referred to by the CDC was published in the journal Pediatrics (a PDF of the article is available here - I find the Pediatrics website difficult to navigate quickly). The study used a very large sample (over 78000 participants) of children from 3 to 17 years of age. It was conducted by randomly dialing U.S. telephone numbers and conducting interviews with the parents who answered the phone. Parents were asked "if they had ever been told by a doctor or other health care provider that their child had 'autism, Asperger disorder, pervasive developmental disorder, or other autism spectrum disorder'. Parents who indicated that they had been given such a diagnosis for their child were then asked if the child currently had autism. When the parent answered "yes" to both questions the child was included in the overall total". The results from this process was that reported 110 in 10,000 respondents indicated "yes" to both questions, resulting in an extrapolated prevelance rate of right around 1 in 100, or 1% of the general population.
When we begin to look at results like this it becomes clear how important the choice of language can be to understanding these types of results. In some cases this is referred to as an "increase in the prevalence" of autism - a phrase which implies that the disorder is increasing in frequency among our population. In scientific writing, however, we are taught to be very careful with our phrasing to prevent such implications, and this is a case in point. The results of this clearly well-done and important study would be more accurately described as providing a change in our understanding about the prevalence of autism.
A study released at nearly the same time as the article in Pediatrics demonstrates this point extremely well. A study completed by the National Health Service in Great Britain looked at rates of autistic disorder among adults in that nation. That study found a prevalence rate of 1 in 100 or 1% - essentially identical to the CDC's findings for children.
The study's design is quite similar to that of the study completed by the CDC, though it uses a much smaller sample (but still over 7,000 respondents) for it's phone survey. However, in the NHS study the researchers also completed the Autism Diagnostic Observation Schedule (ADOS) - the current gold standard for autism assessment - on a subset of the respondents to further evaluate their findings. Even with evaluation using the ADOS the 1% prevalence rate held.
To my knowledge, the NHS study is the first of it's kind to investigate the prevalence of autism among adults - something we certainly must understand before we assume that the actual prevalence is rising. The results of the NHS study strongly support the idea that there are, in fact, a large number of adults in the general population with disorders in the autism spectrum. Further, those numbers are nearly identical to the numbers we are detecting in children today.
That we have not previously looked at prevalence rates among adults points to an area of concern that has been noted among professionals who work with both children and adults with developmental disabilities: Virtually all of the research in autism has been focused upon children. This is certainly understandable, as it's in childhood when we can most help.
Still, those of us who travel in both circles (child and adult treatment) have suspected for some time that there are a large number of undiagnosed adults on the spectrum in a variety of settings. I, along with several other members of the Forest City Team, have had the opportunity to work with adults in both community and institutional residential settings who clearly met the diagnostic criteria for disorders on the spectrum, but who had never been diagnosed (and in many of the cases the symptom presentation was not subtle). This is becoming thankfully less common as understanding of Autism Spectrum Disorder increases among professionals.
These studies add immensely to our understanding of what autism looks like in the general population, and, taken together, will hopefully help us understand where to most effectively focus our efforts to best assist others.
