009 No autism epidemic - Part 3

If we're not in an epidemic, where are all the adults with ASD? That's the trump card in the argument that the current "explosion" in diagnosed cases must be due to an epidemic.

Wouldn't it be wonderful if we could borrow the fancy car from Back to the Future, travel back in time, and study children from an earlier era using today's diagnostic tools? That way, we could cut through all of the arguing about whether today's figures represent broader diagnostic criteria and improved case-finding, or a true increase in prevalence.

Suppose I told you that it's already been done? (without the car!)

England's National Health Service has done what we in America have yet to do: A random sample, door-to-door study of all households in the country, using standard diagnostic tools, to determine the prevalence of ASD among adults. (Autism Spectrum Disorders in adults living in households throughout England. Report from the Adult Psychiatric Morbidity Survey 2007. http://www.natcen.ac.uk/ ) The study excludes group homes for adults with disabilities, healthcare facilities, prisons, and hospitals, limiting eligibility to adults who were living independently in the community. For this reason, the data probably underestimate the true prevalence of ASD. As the gold standard for diagnosis, they used an instrument called the ADOS - the Autism Diagnostic and Observation Schedule. Quoting from their own press release: "This study was the first, anywhere in the world, to measure the prevalence of ASD among adults living in the general population. Previous research has focused on children or on adults in receipt of services."

What they found may surprise you: One percent of adults (1 in 56 adult males, and 1 in 200 adult females) have ASD. Most of them were not receiving special services of any kind, and were unknown to the health- or mental health systems.

There was a slight drop-off in prevalence among subjects in their 50s, 60s, and 70s, but not statistically significant - that is, no greater than might be expected by chance variations in the data. So we can use these data like Doc Brown's DeLorean, to travel back in time to 1940, when these senior citizens were preschool children: the Battle of Britain was raging in the skies over London, America was not yet in the war - and the prevalence of ASD was 1% (or higher, since the NHS survey excluded persons in institutions).

We're going to move along now. There has been a lot of additional research on this topic, for which I refer you to my book. And whenever you hear someone say "We're in an epidemic...." - just remember:
1. An epidemic consists of an increase in incidence (rate of occurrence of new cases), not a rise in prevalence (percent of people diagnosed).
2. Nobody has incidence data. To be fair, although I can show you lots of factors that are sufficient to explain the apparent increase in prevalence without invoking an epidemic, I can't prove we're not experiencing an increase in incidence. But anyone who tells you they have "proof" that we're in an epidemic is - how shall I say it politely? - stretching the truth.
3. Service data cannot be used as a substitute for prevalence - although a lot of people try. There are too many factors impacting service data, none of which have anything to do with the prevalence of ASD.
4. When we look closely at adults, using today's diagnostic standards, we have proof that the prevalence of ASD was at least as high 70 years ago as it is today. Not only is there no proof of an epidemic, there is no "explosion" either.

And now we're going back.....Back to the Future!!

PS: In a delightful twist of fate: Today is the 25th anniversary of the original release of Back to the Future: July 3, 1985! Go and see it!