Analysis of Prevalence Trends of Autism Spectrum Disorder in Minnesota

Abstract

We observed dramatic increases in the prevalence of autism spectrum disorder as a primary special educational disability starting in the 1991-1992 school year, and the trends show no sign of abatement. We found no corresponding decrease in any special educational disability category to suggest diagnostic substitution as an explanation for the autism trends in Minnesota. We could not assess changes in actual disease incidence with these data, but federal and state administrative changes in policy and law favoring better identification and reporting of autism are likely contributing factors to the prevalence increases and may imply that autism spectrum disorder has been underdiagnosed in the past.

Identification and Evaluation of Children With Autism Spectrum Disorders

“…This reflects the phenomenon of "diagnostic substitution," whereby the number of children receiving special education under other categories (primarily MR, speech impairment, and learning disabilities) has decreased over the same time period. In addition, some increase in prevalence may be attributable to inaccuracies in diagnosis for a number of reasons, including labeling biases when schools used less rigorous criteria than those needed for a DSM diagnosis, [44][45][46][47][48] when educational funding trends influenced diagnosis, 49 and/or when parents of children with marginal criteria advocated for the AD label to qualify for supplementary services (eg, year-round schooling) described in the IDEA amendments. 50,51 The impact of these factors on current prevalence estimates has been controversial and illustrates the reason why educational administrative data reported in some studies that receive media attention should not be considered for epidemiologic studies.…”

What's Going on? The Question of Time Trends in Autism

“…Cumulative incidence, defined by many autism researchers as the number of cases diagnosed within a specified age-at-diagnosis window divided by the total population at risk. 20,53,68,73 These studies are most reliably informative with respect to trend, but they are few in number. 4.…”

Autism Spectrum Disorder Reclassified: A Second Look at the 1980s Utah/UCLA Autism Epidemiologic Study

“…Yet, a younger birth cohort from 1995 to 1997, had sufficient documentation of autism criteria in their records to meet case definition by 5 years of age on average (Barbaresi et al 2005). Gurney et al (2003) also found a significant rise in ASD cases within specific birth cohorts temporally associated with federal and state policy changes favoring ASD identification.…”

“…Individuals currently recognized as having an ASD might formerly have received services under a classification of another related condition, such as intellectual disability, speech/ language impairment, or learning disabilities. Most studies supporting (Shattuck 2006;Croen et al 2002;Coo et al 2008) and refuting this theory (Gurney et al 2003;Newschaffer et al 2005) utilize aggregate special education data. Using education records, Shattuck (2006) found a rising number of children with an ASD exceptionality correlated temporally with a declining number with an Intellectual Disability (ID) or Learning Disability (LD) exceptionality.…”