Diagnostic Substitution for Intellectual Disability: A Flawed Explanation for the Rise in Autism
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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.
KeywordsAutism spectrum disorder (ASD) Mental retardation Intellectual disability Diagnostic substitution Time trends Individuals with Disabilities Education Act (IDEA)
We thank the Individuals with Disabilities Education Act for providing the data used in this study.
CN and MB did not have specific funding for this work.
CN compiled the IDEA data, performed all calculations and wrote the Methods and Results. MB conceived of the study and wrote the Introduction and Discussion.
Compliance with Ethical Standards
Conflict of interest
CN and MB declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The ASD and MR counts used in this study involved datasets in which all relevant personal information had been de-identified prior to our activities and in which the data were aggregated by age at the state level. This project therefore did not require institutional review and approval.
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