Saturday, June 14, 2008

1 in 150? Really?

A figure that is much bandied-about by groups such as Autism Speaks, is that one out of 150 people in the United States is on the Autism Spectrum. Michelle Dawson, in an excellent blog entry entitled The Epidemiology of Autism Speaks, shoots lots holes into the arithmetic used by that group. Michelle reports that Autism Speaks has made the remarkable1 claim that one in 150 children is on the Spectrum and that there are 1.5 million autistic children living in the United States. That would mean that according to Autism Speaks, the U.S. has over 225 million children. (!)

This has left me more than a bit curious. Just how accurate is the 1 in 150 statistic? Is it true? It is repeated in news stories about Autism so often, it sounds like an incantation used to make the story more authoritative and believable. But where did this number come from? Was there any research to back it up?

In the search for evidence, I turned first to the National Institute of Mental Health's website. Finding information about autism was simple. Going through the online booklet on Autism, I found this:

Prevalence studies have been done in several states and also in the United Kingdom, Europe, and Asia. A recent study of a U.S. metropolitan area estimated that 3.4 of every 1,000 children 3-10 years old had autism.

This was in the first paragraph of the section What are the Autism Spectrum Disorders? Wait, 3.4 out of 1,000 children? Doing the math, that works out to 0.0034; 1 out of 150 is 0.0066. The quoted study indicates that the rate may be half of what the conventional wisdom holds.

Looking through the references, I found the study they cited: "Prevalence of Autism in a US Metropolitan Area"2, published in the Journal of the American Medical Association. The article can be found here on the Journal's website. The researchers studied the records of children aged 3 to 10 in five counties in the Atlanta area in 1996.

This paper contains several revealing things:

  • At the time of the article's publication (1 January 2003), there have been only four studies of the prevalence of ASDs in the United States. Three of them were conducted in the 1980s and early 1990s. The last one was done in 19983. The authors confess that because of this, little is known about the actual number of people on the Spectrum.
  • In the first three studies, they found a rate of 4 out of 10000. The 1998 study found it to be as high as 67 per 10000, but the article's authors warn that that figure may be badly skewed.
  • The numbers they cite from other studies performed in the US and abroad are wildly different. Studies from before 1985 claim that only 4 to 5 out of 10000 are on the Spectrum, with 2 out of 10000 having the classic Kanner's autism. Recent work in the UK suggests that it could be as high as 62.6 per 100004.
  • In their study of Atlanta-area children, the authors found that the prevalence of ASDs among Black and White children were the same, 3.4 out of 1000.
  • The authors did not actually examine the children. They relied on school records and the written assessments of psychiatrists, pediatricians, neurologists and other mental health professionals to determine if a child is autistic. By claiming that this was a public health issue, they were able to obtain these records without the parents' permission.

The UK study, published in 2001, claims a rate that is close to the 1 out of 150 figure. The trouble is that they used a much smaller sample than the 1996 Atlanta study did (about 10%) and were more inclusive in what they considered to be an ASD.

What does this all mean? The 1 in 150 meme is a product of lazy thinking and lazy fact-checking. It only took me a few minutes to find contrary data on the NIMH website and then find the referenced research. I am reminded of another phony statistic that had been tossed around for a long time, namely that one out of every ten American men are gay or leaning towards being gay. This figure is attributed to Alfred Kinsey's study, Sexual Behavior in the Human Male, which was written in 1948. Kinsey's methodology was extremely flawed; his data collection relied on interviews with volunteers, many of whom were or had been prisoners. This ten percent figure had a nice ring to it, and because of the success of Kinsey's books, it entered the public consciousness and never really left.

In the same way, 1 out of 150 is an easily understood number that anyone can repeat without actually giving it any thought. It has all of the hallmarks of a made-up statistic that may have roots in legitimate research, but has taken a life of its own.


  1. I have always liked how the United State Supreme Court uses the word 'remarkable'. In written opinions, the justices use it as a term of polite damnation. It would not do for them to say that an argument was 'stupid' or 'a bunch of horseshit': that would be unsubtle and rude. Instead, they will call a ridiculous argument 'remarkable' and leave it to the rest of us to fill in the blanks.

  2. Yeargin-Allsopp M, Rice C, Karapurkar T, Doernberg N, Boyle C, Murphy C. "Prevalence of Autism in a US Metropolitan Area". The Journal of the American Medical Association.. 2003 Jan 1;289(1):49-55

  3. Bertrand J, Mars A, Boyle C, Bove F, Yeargin-Allsopp M, Decouflie P, "Prevalence of Autism in a United States Population". Pediatrics (2001) 108:1 1155-1161

  4. Chakrabarti S, Fombonne E. "Pervasive Developmental Disorders in Preschool Children". The Journal of the American Medical Association. (2001) 285:3093-3099.
    The article may be found here.


jonathan said...

Actually the 1 in 150 figure comes from a study that the CDC published last year which was an average of various metropolitan areas on the prevalence of autism among 8 year olds. As you correctly point out, this figure has never been really replicated in the rest of the epidemiologic literature on autism. Assuming autism rates have remained stable throughout history which may or may not be the case then we can presume that if the CDC study is correct than 1 in 150 persons across all age groups would have some sort of autism spectrum disorder.

The statement of the president of autism speaks about 1.5 million children was clearly a gaffe on his part. But people are known to make mistakes. Also one of the problems is that groups like autism speaks want to keep autistic adults such as myself as invisible as possible because they don't want people to know what the true grim prognosis for us is. They want to treat us like peter pans.

Anonymous said...

a little epidemiology of my own I know 5 kids with autism under 6 years old (not aspergers) and I don't know 100 kids.
I must be plain unlucky

R. Gerald Lovejoy said...

Regarding anonymous' comment:

That is not how statistics works. The 1996 Atlanta study worked with a little less than a thousand autistic children out of a population of over 250,000 elementary school students in the Atlanta area.

Your knowing five children with Autism out of a population of less than a hundred (you did not say how much less) is entirely anecdotal. The sampling and the population are not large enough to be able to draw any sort of statistically significant conclusions.

R. Gerald Lovejoy said...

Regarding jonathan's comment:

All of the scare stories that Autism Speaks tosses around is fantastic for fund-raising purposes. Nothing motivates donors more than a lot of superheated rhetoric about how the opposition or the 'enemy' will be able to do all sorts of dastardly things if they do not send in that check.

Groups like Autism Speaks capitalize on the fears of parents. Autistic adults are not their target audience, which is why they brush us off. Austism Speaks is in kind of a weird position: they are trying to maintain a veneer of scientific respectability while pursuing a eugenicist agenda, while relying on the support of militant parents of ASD children, many of whom support the mercury superstition.