1) The characteristics of the autistic population have changed over time. Severity indicators are dropping consistently as apparent prevalence rises. Comparing numbers from one year to the next is like comparing apples and oranges.
2) The 'epidemic' is geographically isolated. There is evidence of a catch-up factor between regions, as well as evidence of group inequivalence between regions.
3) There is no evidence that objectively diagnosed co-morbidities of autism have been on the rise. Existing data show that this is not the case at least for epilepsy and mental retardation.
4) There is evidence of diagnostic substitution, in particular from mental retardation and learning disability.
5) There is evidence of increasing recognition of autism within the population with mental retardation.
6) There is no evidence of incidence drops which may be correlated to removal of possible environmental triggers.
Some of these observations have already been made in the mainstream literature. See for example:
- Laidler, US Department of Education Data on "Autism" Are Not Reliable for Tracking Autism Prevalence (2005).
- Shattuck, The Contribution of Diagnostic Substitution to the Growing Administrative Prevalence of Autism in US Special Education (2006).
The staff of California DDS Data Extraction itself is well aware of many of these facts and of the misuse of caseload data to determine prevalence and incidence numbers. This is clear from communications I have received from CDDS:
I have argued many of these points myself in several blog entries. Although some bloggers have disagreed with my conclusions, no real rebuttals have been posted.
- No Autism Epidemic: Summary of the Numerical Evidence.
- CDDS Data 101.
- "Like Missing a Train Wreck" - By The Numbers.
- Regional Differences and Quarterly Growth Due to Two Factors.
Evidently, citing prevalence numbers is no longer sufficient, for the reasons already given. At this point any claim of 'autism epidemic' may be described as naive, uninformed, far-fetched and unsubstantiated. Epidemic proponents need to come up with new evidence. And given that this is an extraordinary claim now, it will require extraordinary evidence.