Diagnostic Substitution for Intellectual Disability: A Flawed Explanation for the Rise in Autism.
Rising autism numbers aren’t just re-labeled ID cases—ID prevalence stayed flat while autism soared.
01Research in Context
What this study did
García-Villamisar et al. (2017) pulled U.S. special-education counts from IDEA. They looked state-by-state at autism (ASD) and intellectual disability (ID) labels from 2000-2010.
They asked a simple question: when autism numbers went up, did ID numbers go down? If they did, it would support the idea that kids once called ID are now called autistic.
What they found
The big states that drive national totals showed flat ID prevalence while autism kept climbing. The mirror-image swap just wasn’t there.
The authors conclude that diagnostic substitution—switching an ID label to an ASD label—cannot explain the autism surge.
How this fits with other research
Watt et al. (2026) looked at the same IDEA file and saw the opposite: a 331 % ASD jump paired with a 64 % ID drop. The two papers contradict, but they used different age brackets and year ranges; tiny method choices flip the answer.
Hé lène et al. (2007) had already shown that earlier detection, not new cases, pushed numbers up. García-Villamisar et al. (2017) add that those extra cases are probably not recycled ID labels.
Lai et al. (2013) found both ASD and ID rising together in Taiwan. That pattern matches D et al.’s U.S. finding and extends it across the Pacific—suggesting global trends rather than local coding games.
Why it matters
When you see a child with an autism label, do not assume ID has been ruled out. Flat ID rates mean many kids still carry both diagnoses or remain mislabelled. Always run full cognitive and adaptive tests. Update your file review checklist: look for past ID eligibility, re-test if scores are old, and write goals that target the true deficit—whether it’s social, cognitive, or both.
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02At a glance
03Original abstract
Time trends in autism spectrum disorder (ASD) and intellectual disability (ID) prevalence from the United States Individuals with Disabilities Education Act data were computed from 2000 to 2011 for each state and each age from 6 to 17. These trends did not support the hypothesis that diagnostic substitution for ID can explain the ASD rise over recent decades, although the hypothesis appeared more plausible when the data were aggregated across all states and ages. Nationwide ID prevalence declined steeply over the last two decades, but the decline was driven mainly by ~15 states accounting for only one-fourth of the U.S. school population. More commonly, including in the most populous states, ID prevalence stayed relatively constant while ASD prevalence rose sharply.
Journal of autism and developmental disorders, 2017 · doi:10.1007/s10803-017-3187-0