|Regional Center||Autism-Epilepsy Ratio||Epilepsy||MR||Severe Behaviors||In MR Population|
Table 1 shows that there is inequivalence between Regional Centers, but it is not as straight forward as the inequivalence observed in the state-wide quarterly data. A pattern emerges, however, if you look at the proportion of autistics in the population with mental retardation. Except for San Diego (SDRC), which does appear to be behind in criteria, it would seem that differences in autism rates can be explained by how many clients evaluated as having mental retardation are also determined to be autistic.
In order to test this hypothesis, let us adjust the autism caseload by assuming that 7% of all clients with mental retardation are also classified as autistic (as this is roughly the state-wide average). We will then see what the proportion of MR and lack of it among autistics might be given this assumption.
|Regional Center||Autism-Epilepsy Ratio||MR||No MR|
Table 2 looks more like the state-wide time-based data, as we would expect. The consistency of these results does two things:
- It suggests that our assumption is probably valid. That is, the proportion of autistics in the MR population throws off the numbers, and differences in this proportion are apparent, not actual.
- It suggests that the proportion of autism in the non-MR population varies from region to region simply due to inequivalence, i.e. differences in criteria between regions.
These findings lead me to come up with a more specific model to explain both the explosion in diagnoses since the early 1990s and regional differences in apparent prevalence. The model involves two factors:
1) There is increasing recognition of autism in the population with MR. [This was already noted in "Like Missing a Train Wreck" - By The Numbers].
2) There is increasing recognition of autism in the population without MR.
These two factors act somewhat independently. As time goes by, both occur simultaneously. But they may vary independently from region to region. For example, San Diego (SDRC) is considerably behind the average Regional Center in Factor # 2, but is considerably ahead in Factor # 1. Fresno (CVRC) is considerably behind in both factors. West LA (WRC) is considerably ahead in both.
In retrospect, these two factors are obvious. But note that a common error is to assume that 'broadening criteria' includes only Factor # 2.