Friday, July 06, 2012

Rechecking autism prevalence

kw: autism, statistics

This morning I heard an ad I have heard many times, in which Curt Schilling ends by saying, "The chances of having a son with autism: one in 110." I decided to look into it. My sources for the statistical information below are this publication by C.J. Newschaffer et al and this Wikipedia article.

The public perception of autism was greatly improved by Dustin Hoffman's portrayal of a high-functioning autistic man in The Rain Man. The character of Raymond was based on Kim Peek, who died in 2009. However, not many autistic persons have genius-level abilities of memory or calculation. Kim Peek is an example of an autistic savant, and he was somewhere in the middle of the "autistic spectrum".

The autistic spectrum comprises three defined syndromes:
  • Classical Autism describes people who cannot form relationships, may never recognize other people, and communicate poorly or not at all.
  • PDD-NOS, Pervasive Developmental Disorder Not Otherwise Specified, is a wide-ranging slush bucket of syndromes that include some, but not all, characteristics of classical autism. Some cases are more profoundly affected than others, and many or most instances of autistic savants are found here.
  • Asperger Syndrome is the highest-functioning type. A few AS persons are savants, but the syndrome as a whole describes people who are very focused on one or a few interests, may become very expert in those interests, are able to converse and form relationships, but have certain autistic behaviors.
I know three men with Asperger syndrome. One in particular is a young man who went to high school with my son. He and I were assigned to collect tickets for a football game. He is extremely interested in weather, and when he learned I had lived in Oklahoma, he quizzed me extensively about my experiences of powerful thunderstorms and tornadoes. My son said he is the school weatherman, always glad to provide a forecast, though perhaps in greater detail than you have time for. Unlike people with classical autism, he could look you in the eye.

I also know two young men who are profoundly autistic. One is the son of a couple who belong to the local Mensa chapter. He is barely able to recognize his parents, cannot speak, and the slightest frustration causes him to roar like an animal. It seems his mother can guide his behavior a little, in that he understands a few of the words she says. His perception of English is probably below that of a house pet.

In spite of several decades of study, the actual incidence of these disorders is only poorly known:
  • Autism: 1 or 2 per 1,000. The average of a number of studies is near 1.7 per 1,000.
  • PDD-NOS: 3.7 per 1,000.
  • Asperger: About 0.6 per 1,000.
These add up to very nearly 6 per 1,000, or 1 out of 167. There is an added fact. Across the spectrum, males outnumber females 4.3 to 1. In my reading I didn't get a clear feeling whether one of the three areas hits females harder or less hard than males, in proportion, so I just analyzed these data based on the 4.3:1 figure for all. I find that the totals for the entire spectrum are 1/440 for girls and 1/103 for boys. The ad with Curt Schilling is correct in this regard, as it specifically says "son". The spectrum splits up this way:
  • Autism: 28%, or 1/1580 for girls and 1/370 for boys.
  • PDD-NOS: 62% or 1/710 for girls and 1/165 for boys.
  • Asperger: 10% or 1/4,400 for girls and 1/1,030 for boys.
If there is a silver lining in this dark cloud of affliction, it is that nearly 3/4 of children on the autism spectrum will be able to relate to others at a useful level. The tragedy is that of 4.1 million babies born yearly in the U.S., nearly 25,000 will be afflicted with an autistic spectrum disorder, and nearly 6,900 of them will be classically autistic and require lifelong care.

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