Tuesday, August 10, 2010

Does John Elder Robison Understand Autism Prevalence?

John Elder Robison is a "bestselling author, autism advocate, and founder and owner of J E Robison Service Company of Springfield, Massachusetts" and serves on the the scientific advisory board of Autism Speaks.

Mr Robison is in a position to help decide what research Autism Speaks should fund, so I would expect him to be quite knowledgeable when it comes to the science of autism. Yet from some of his recent comments, I am not sure that he grasps the science behind one of the fundamental questions about autism - is autism increasing?

Below is something that Mr. Robison recently wrote about the increase in autism as part of a larger conversation. I am not going to address the main points of the discussion because Jonathan already did a good job of that at Autism's Gadfly. Instead, I want to focus on his statements about the apparent increase in the rates of autism -
The 600% thing may be misleading, but it's still real. Is some of it caused by more inclusive standards in the new DSM? Sure. Is some caused by much greater public awareness? Sure. Is some caused by increases in certain kinds of autism . . . probably. There have not been any studies to clarify this point because there is no data on the prevalence of certain kinds of autism in years past - there's only data on the whole spectrum. It's very hard to explain the reason for the increase and no one has figured out a way to determine if certain conditions like childhood disintegrative disorder are increasing, or just more visible. The same can be said for Asperger's.
The 600% refers to the apparent increase in autism rates over the past decade or so. Now, I have to give Mr. Robison credit for actually admitting that "certain types of autism" are "probably" increasing. But all of the credit goes bye-bye when he says (presumably with a straight face), that increases in conditions like childhood disintegrative disorder might be responsible for part of the increase and that there is no data on the breakdown of the spectrum.

For those of you who don't know, childhood disintegrative disorder (CDD) is a very rare condition that is one of the five conditions that together make up the pervasive developmental disorders - more commonly known as the autism spectrum.  And while it is true that children with CDD do look a lot like children with autism, there are some very significant differences.  Children with CDD have an extended period of "normal" development (at least 2 but no longer than 10 years) before undergoing a very significant (and most times very rapid) regression where previously acquired social, communication, and motor skills are lost.  After the regression, these children do show the same behaviors as other forms of autism but, unlike other forms of autism, once skills are lost, they are typically never regained.

To put it bluntly, when your child goes from being a bright talkative five year old to being a child with an intellectual disabilty who no longer talks, looses motor skills, and no longer has bladder control and stays that way for the rest of their life, that would be CDD.

CDD can make even lower functioning autism look good by comparison.

The strange thing is that it isn't like we have no idea how how (un)common CDD is. All the way back in 2002, there was a review article published that cited prevalence estimates from 1966 onward and came up with a figure of about 1.7 per 100,000 for CDD.  Compare that to the recent CDC figure of about 910 per 100,000 for all types of autism.

Even if CDD has seen the same massive increases that other forms of autism did over the past decade, we are still only talking about 10 per 100,000 compared to 910 per 100,000.  But I have not been able to find any published work that even suggests that the rate of CDD could have increased this much and, as recently as 2009, the 1.7 per 100,000 figure is still being used.

So, in other words, if you ignore all of the data that has been published on the subject and make some huge leaps of faith, you could possibly conclude that about 1% of all current autism cases are CDD.  However, a much more realistic scenario is that CDD hasn't increased so drastically and makes up less than 0.5% of all autism cases.

In either case, it is highly unlikely that an increase in CDD is a major (or even minor) factor in the 600% increase in autism.

Which leads into the second problem with what Mr. Robison said - that we don't have a clear picture of what types of autism are increasing.  If you even do a quick search, you can turn up several places where breakdowns have been done. Take for example this study from 2009 that clearly gives a breakdown between the types of autism -
This article reviews the results of 43 studies published since 1966 that provided estimates for the prevalence of pervasive developmental disorders (PDDs), including autistic disorder, Asperger disorder, PDD not otherwise specified, and childhood disintegrative disorder. The prevalence of autistic disorder has increased in recent surveys and current estimates of prevalence are around 20/10,000, whereas the prevalence for PDD not otherwise specified is around 30/10,000 in recent surveys. Prevalence of Asperger disorder is much lower than that for autistic disorder and childhood disintegrative disorder is a very rare disorder with a prevalence of about 2/100,000. Combined all together, recent studies that have examined the whole spectrum of PDDs have consistently provided estimates in the 60-70/10,000 range, making PDD one of the most frequent childhood neurodevelopmental disorders.
Notice how the two types of autism that Mr. Robison called out - CDD and Asperger's - are both listed as being rare relative to a overall rate of 60-70 per 10,000.  The bulk of the cases of autism in this review are either PDD-NOS or classic autism.

The current rate for the entire spectrum is about 90 per 10,000 and, as the CDC said in its most recent report, the increase from the earlier 60 per 10,000 isn't all in the conditions like Aspergers.  As a matter of fact, the increases are somewhat spread out but the classic autism category might show a greater increases than the other conditions -
The widening of diagnostic criteria over time to include persons who are more mildly affected has been suggested frequently as a factor influencing increases in ASD prevalence. (snip) However, in this analysis, a clear shift was not identified from 2002 to 2006 in the use of the more broadly defined ASD diagnoses. In fact, for several sites, increases were recorded in the use by community professionals of the autism diagnosis rather than the other ASD diagnoses. Another indicator of identifying children on the more mild end of the spectrum would be a differential increase in prevalence among children with borderline or average to above-average cognitive functioning. Although the overall pattern among these higher cognitive functioning groups indicated substantial increases in ASD prevalence, increases also were observed among children with cognitive impairment. Increases varied across sites, and a clear pattern did not emerge that would permit attributing the majority of the increase in ASD prevalence to the use of the broader ASD spectrum.
So for Mr. Robison to suggest that any significant part of the increase in autism is due to CDD or that we have absolutely no idea what type of autism is increasing is disingenuous at best and intellectually dishonest at worst.  What is he doing serving on the scientific committee of Autism Speaks if he can't even get the basic facts right?


  1. Where would I be without you to correct me? I know there have been studies that show increases in autism diagnosis rate that exclude broader diagnostic criteria, etc.

    I absolutely believe autism has or is becoming more common. The question is, what are the numbers? No consensus exists because of the number of factors involved.

    For every person who "knows" the answer in this area there is someone else with an alternate certainty.

    So what do you want to make of it? Bring me a grant proposal to get new and substantive insight into what's increasing and where, and I'll read it. And my interest in studies that can lead to help for people who live with all kinds of autism still stands.

  2. The larger issue here is accuracy in discussions about the science of autism. When you go onto an online forum and suggest that CDD is responsible for a part of the increase of autism and that "there have not been any studies" on where the increase is, you are simply being inaccurate and presenting a false picture of what the data is.

    Doing so is harmful to everyone involved - especially to those that you are saying that you want to help. If we continue forward with our little half truths and preconceived notions, we are going to go nowhere fast. The only way forward is to work with accurate information.

    If you knew that there are studies that show increases in the narrow categories alone, why on earth would you say that these studies do not exist in another forum? Was that just for the benefit of your audience or did I misunderstand what you were saying?

  3. MJ, I am not aware of any generally accepted studies that are able to break down increases in rates of autism outside the factors we've discussed.

    There is certainly a widespread perception that there is an increase, and of course the statistics do support that conclusion, but how much seems unquantifiable.

    I chose the CDD example because it's a very serious condition and a number of doctors cited it to me as something they see more of. You are right; it's rare, so "seeing more might mean you see three cases instead of two. No one has hard numbers but more that one person has cited that example among others.

    You can make of that what you will. I have the sense that the increase is real, and that's about as far as it goes. Beyond that there is not no unraveling the various legitimate explanations for various parts of the increase in the raw numbers.

    I don't think any disservice is done to anyone by stating that.

  4. Just off the top of my head, there is this study - http://www.ncbi.nlm.nih.gov/pubmed/19737791 - that found that only a quarter of the increases in autism rates in California were due to diagnosing practices. You might not call that generally accepted, but the results do speak directly to the point. I know there are other studies like this out there, but I would have to go dig up the references to them.

    We can quibble about how much of the increase over the last whatever time period was due to social factors but the point remains that at least a part is likely to be a true increase. Does it matter if the increase due to this factor is *only* a 100% or 200% change? An real increasing rate of autism implies a cause of autism which means that we have a problem.

    As for the CDD, you might very well be right that it is increasing but, as I pointed out above, even if the increase is huge it can't play even a minor role in the increase of autism. But, if a substantial part of the increase is due to CDD then I would say that means that social factors play even less of a role than is commonly thought.

    I would agree that that there is no disservice done by stating that there are a lot of unknowns when dealing with autism prevalence, and if you had said that I would not have said anything. If you had even said that there are a lot of unknowns but you think that the vast majority of the increase was due to social factors, I would have disagreed but not said anything.

    The disservice is when you don't cleanly separate your opinion from science or misstate the science. And maybe you didn't mean to do that or maybe I am just misunderstanding what you were saying, but that is how it looked to me.

  5. Such an interesting and important post. I've been learning a lot from your blog - you've really helped to refine my own understanding of autism. Thank you.

  6. Thanks, I'm glad you like the site.