How “Educational Assessments” Skew Autism Prevalence Rates

James R. Laidler, M.D.
September 15, 2004

During an Individual Education Plan (IEP) meeting with our local school district, one of the teachers suggest that my younger son was autistic. This surprised me because we had just provided a letter from a well-respected developmental pediatrician that specified why the boy not meet the diagnostic criteria for autism. In response to my concerns, the teacher and school psychologist explained that he met the criteria for autism as determined in Oregon under a federal law called the Individuals with Disabilities Education Act (IDEA).

In response to this law, school districts have been assessing (not diagnosing) “autism” in children since 1992. Because the eligibility category under IDEA has the same name as the medical diagnosis, there has been a lot of confusion and unnecessary worry. Medical diagnosis and educational assessments have different purposes. Medical diagnosis are made in order to (a) determine the best treatment strategy, (b) advise what to expect in the future (prognosis), (c) allow data collection and statistical analysis, and (d) support billing of third-party payers (insurance), whereas educational assessments are designed to determine eligibility for special educational assistance.

Dozens of medical diagnoses can be used to describe a child with some or all of the features of autism (e.g. autism, pervasive developmental delay, Asperger’s Syndrome, Rett Syndrome, Fragile X, multi-system developmental delay, etc.). The IDEA has only nine eligibility categories, only a few of which actually apply to children with autism. Although the educational assessment may suggest which types of educational assistance may help an individual child, the federal law (US Code, Title 20, Chapter 33, Section 1414) states that specific needs (not eligibility) should determine what services are offered. As a result, the educational assessment emphasizes eligibility rather than diagnostic accuracy. This wouldn’t be a problem except that the education “diagnoses” are reported to the U.S. Department of Education (USDE) and then used by others to support their positions on autism.

Further clouding the issue, each state sets its own assessment standards and procedures, within the limits of the IDEA. Most states have followed the diagnostic guidelines in the American Psychiatric Association’s Diagnostic and Statistical Manual (4th edition)—the “DSM-IV”—but others have created assessment guidelines that are very different. However, many of the children assessed as autistic by the schools do not meet the DSM-IV criteria for autism.

Figure 1 illustrates the number of autistic children reported by the various states’ education departments. It shows that the majority of states are clustered together, but a few stick out above the crowd. To make this clearer, figure 2 shows the three highest states, the three lowest and the three in the middle—along with the prevalence in California and the US as a whole. Note that Oregon’s autism prevalence has been consistently between two and three times the national average and that Minnesota has recently risen to that level. At the same time, the prevalence of autism in Washington (immediately to the north of Oregon) and California (to the south) are not significantly different from the US average.

So, what is happening in Oregon and Minnesota? The theories of pollution, lead poisoning or mercury poisoning cannot explain why they have a higher prevalence of autism than Louisiana, New Jersey, Texas or Mississippi. Oregon and Minnesota do not have higher vaccination rates than the rest of the country, and their parents are not any worse or any better than the rest of the US. The difference occurs because the Individuals with Disabilities Education Act lets the individual states decide the details of eligibility. They cannot be more restrictive, but they can be more permissive. As a result, most states either use a slight modification of the DSM IV criteria or have the diagnosis of autism made by a qualified medical professional. Washington does this, for example, but Oregon and Minnesota use much broader criteria.

You can see how this works by comparing their sections dealing with social and behavioral abnormalities that are characteristic of autism:

  • The DSM IV lists four specific types of abnormal social behavior (e.g. “lack of social or emotional reciprocity“) and requires that at least two of them to meet the social impairment section of the diagnostic criteria.
  • The Minnesota statute lists broader social abnormalities (e.g. “may appear to prefer isolated or solitary activities”) and requires two of them to meet the criteria.
  • The Oregon statute is even more vague: Its social impairment criteria simply states, “Impairments in social interaction” and leaves the interpretation up to the evaluator.
  • In contrast, Washington defines autism much more rigorously by requiring “a specific diagnosis, by a board-eligible psychiatrist or licensed clinical psychologist, of autistic disorder.”

There is a definite connection between a state’s autism prevalence as reported by the USDE and the criteria that state laws have established for autism eligibility under IDEA. However, because the IDEA criteria have no demonstrated relationship to the medical diagnosis, the USDE numbers are not valid for comparing one state to another or even one year to another within a particular state. This does not “prove” or suggest that autism prevalence is not increasing. However, it does mean that the USDE numbers on autism, while extremely convenient, should not be used to track the prevalence of autism in the United States.

This article was posted on September 15, 2004.