Tag Archives: autism prevalence

The Hidden Horde Theory

I was writing previously about my friend who challenged me, saying she thinks that there isn’t a real increase in autistic kids–just an improvement in diagnosis.

There’s a logical argument that refutes her claim. It’s called the Hidden Horde Theory.

I am reading a book, Changing the Course of Autism by Bryan Jepson, MD.  This book is full of information on studies related to autism, and is particularly aimed at physicians. However, it is readable by a lay person and in fact should be read by anyone puzzling over what is known about autism at this point.

Jepson presents plenty of statistics, including a detailed study of kids in California, that makes it very clear that there are many, many autistic kids now–one in 166 in the US as reported by the Center for Disease Control in 2004. The CDC also reported that one child in six is being diagnosed with a developmental disability or behavior problem.

Here’s the conundrum: if there were that many undiagnosed autistic kids 30 years ago, there would be a horde of them out there as undiagnosed or misdiagnosed adults now.  “Autism is disabling, and individuals would end up where society deposits the mentally ill: outpatient psychiatric clinics, mental institutions, homeless shelters, or prisons,” says Jepson (p. 37).

Nylander and Gillberg screened adults in Sweden at outpatient psychiatric facilities looking for undiagnosed cases of autism.  They assumed they would find some. In fact they found 19 people who met autism criteria who were previously undiagnosed.  But that brought the prevalence rate to only 2.7 per ten thousand, similar to other developed country population prevalence rates for autism before 1980.

No one has found the hidden horde, although others besides Nylander and Gillberg have looked, says Jepson.

Meanwhile, the number of autistic kids now diagnosed is going to overwhelm our social care systems.  Even if no more autistic kids were born starting now, the long-term care for those already leaving (estimated at $3.2 million per person over a lifetime) could absorb, and then bankrupt, the federal social services budget, says Jepson (p. 40).  As of September, 2006, the number of people with full-criteria autism receiving services in California was 31,853.


Jepson, Bryan, MD, and Jane Johnson, Changing the Course of Autism, Sentient Publications, 2007, 354 pages

Nylander L, Gillberg c. Screening for autism spectrum disorders in adult psychiatric outpatients; a preliminary report. Acta Psychatr Scand 2001 June;103(6):428-34.