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Study: Autism Rates Tied to Changes in Diagnostic Practices
> 4/9/2008 1:51:12 PM

The rise of autism diagnoses since 1980 panicked parents and spurred researchers to look for environmental causes. It cannot be disputed that the number of recognized autistic individuals is rising, but that does not prove that autistic cases are actually more prevalent. Many psychologists have speculated that the change can be attributed solely to new diagnosing practices, but in the March 2008 issue of Developmental Medicine & Child Neurology we finally see quantitative evidence for that argument.

Professor Dorothy Bishop led a team of researchers from Oxford in a reinvestigation of older cases - from 1986 to 2003 - of developmental language disorders. These diagnoses are given when a child shows a marked difficulty using or understanding spoken language. The researchers focused on these disorders because their symptoms overlap with the autistic spectrum, and because a 2003 study by Dr.� Hershel Jick used the General Practice Research Database to find a direct correlation between falling language disorder diagnoses and rising autistic diagnoses. This see-sawing is certainly suspicious, but it is not rock-solid proof by itself that one diagnosis was replaced by the other.

Dr. Bishop gathered the necessary proof by re-opening the cases of 38 adults diagnoses with language disorders as children. The subjects were given the Autism Diagnostic Observation Schedule - Generic and their parents completed the Autism Diagnostic Interview - Revised. Eight subjects met the current criteria for autism for both tests, with four more coming down somewhere lower on the autistic spectrum. This uncovers a large percentage of diagnoses that would have been different if conducted under today's guidelines.

Dr. Bishop's study is small, but when combined with the work of Dr. Jick and others, it lends considerable credence to the idea that the "autism epidemic" could be an illusion caused by changing diagnostic methods. More research is needed to determine just how many pre-1980 diagnoses would be different under current methods, but whether the numbers are rising or not, the high toll of the disorder is quite real and still merits considerable attention.

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