Originally Posted by teacozy
"RESULTS. The average administrative prevalence of autism among children increased from 0.6 to 3.1 per 1000 from 1994 to 2003. During the same period, the prevalence of mental retardation and learning disabilities declined by 2.8 and 8.3 per 1000, respectively. Higher autism prevalence was significantly associated with corresponding declines in the prevalence of mental retardation and learning disabilities. The declining prevalence of mental retardation and learning disabilities from 1994 to 2003 represented a significant downward deflection in their preexisting trajectories of prevalence from 1984 to 1993. California was one of a handful of states that did not clearly follow this pattern."
So how do you explain the drop in prevalence of mental retardation? Is your theory that vaccines protect against mental retardation?
A big part of the reason that rates of intellectual disability has dropped is because of the use of adaptive behavior as a qualifying criteria in addition to IQ scores. With IQ scores alone, a disproportionate level of low SES and minority children where labeled as intellectually disabled who were completely functional outside of schools. The inclusion of adaptive behavior is the biggest reason for the drop.
Another reason for the drop is prenatal testing and abortion. In 85% of cases where a pregnant woman learns that her baby has Down's (which is the leading chromosomal cause of intellectual disability) she aborts.
The rates of PKU, Rh, and neural tubes defects (all of which are associated with intellectual disabilities) have also gone down due to medical intervention.
Fetal alcohol syndrome is the leading cause of preventable intellectual disability, and I can't find stats on whether it is increasing or decreasing. However, since the surgeon general only added their warnings in the 80's, one would hope that rates of intellectual disability caused by drinking have dropped since then.
But to look at rates of intellectual disability and think that the ONLY reason they are going down is increase identification of autism is just ignorant, in the true sense of the word. There are many, many factors at play.
The prevelence of LDs is very, very complicated because we keep switching how we define and test for it. It is a completely social defined disability (as opposed to being blind or deaf that is the same across cultures and time). But in the period referenced in this study, response to intervention (RTI) was added to the federal definition. So children who would have been required to be labeled as LD to recieve assisteance before this change are now given assistance without any label through RTI. For many of these students, this is enough and they are never labeled. This is a massive shift. It is also possible that some kids were IDed with LD during the whole language movement who really just needed explicit instruction.
Back to autism.
One of the ways they decide prevalence statistics is how many kids received services at school based on certain diagnosis. This is easily tracked. IDEA defines which categories can receive services under.
Autism was only added as a category in IDEA n 1990. Before that, children with autism frequently had other labels in school, such as intellectually disability, other health impaired, speech or language impairment, or emotionally disabled. The reason that it was added as a category is because the rates had already gone up. It used to be very rare, and now it isn't.
Of course creating an actual category in IDEA switched kids from other categories. But that doesn't account the rapid increase, the actual changes in demographics that made creating that category make sense.
In special ed, autism is the fastest growing category. If this were ONLY a matter of switching how kids are categorized, then we would have seen a huge jump in the first few years after the category was created, but then it would have taped off to whatever the "real" level is. It's been 24 years and there isn't a tapering off -- instead the rates continue to rise.
And no body really knows why.
A lot of the information in the post came from "Mental Retardation: An Introduction to Intellectual Disabilities" by Beirne-Smith and from "Exceptional Children: An Introduction to Special Education" by Heward.