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.
- 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.
- 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
- 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
- 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.