CDC measured its own method change before publishing across it
When CDC changed what counts as an autism case in 2018, it published a bridge study in the same report: about the same for 2014, 7% lower for 2016, and 86% of children met both definitions.
We have not finished checking this source. No judgement either way. how we score evidence
Caveat on this rating: The bridge-study numbers cut against a tidy narrative in both directions, so both halves are printed here and neither may travel alone. The 2018 case-definition change is a genuine construct break, and the series must not be spliced across it. And the change's measured size - approximately no difference for 2014, 7% lower for 2016, with about 86% of children meeting both definitions - is far too small, and points the wrong way, to explain the 18.5 to 23.0 per 1,000 step it sits under. Quoting either half without the other misleads. One scope limit: the bridge analysis compares the two definitions on ADDM data for 2014 and 2016 only, and is not a general estimate of the change's effect in later surveillance years.
Through surveillance year 2016, trained clinician reviewers applied operationalized DSM criteria to abstracted record text, and a child could be counted with no autism diagnosis recorded anywhere. From 2018 the rule became simpler and different: a child is a case if the system ever labelled them - a diagnostic statement in a comprehensive evaluation, an autism special-education eligibility, or an autism ICD code. That is a change of construct, from "the records describe autism" to "the system ever said autism."
Significant findings
The unusual part is what CDC did with it. Rather than change the definition and leave readers to guess at the step, the agency ran both definitions over the same data and published the result inside the report that introduced the change: "An analysis using data from ADDM Network surveillance years 2014 and 2016 compared the case definitions and found that, compared with the overall ASD prevalence using the previous case definition, ASD prevalence using the new case definition was approximately the same for 2014 and 7% lower for 2016. ... Approximately 86% of all children who met either the previous or new case definition met both case definitions."
So the break carries its own size, and two things follow that have to travel together. The break is real, and a chart running a single unbroken line through 2018 is joining two different constructs. And the break is small, and pointed the wrong way, to carry the step it sits under - the overall figure went from 18.5 to 23.0 per 1,000 across that boundary while the definition change itself was measured as neutral to slightly negative.
The change also had a direction beyond its size. CDC noted the new definition "could be more likely than the previous one to include children of lower SES because the previous case definition excluded children without sufficiently detailed records." A measurement change can alter who becomes visible, not only how many are counted, and that is a different kind of fact about a rising number. The annotated series, with every break drawn as a break, sits at www.resolv.social/topics/how-autism-got-counted.
Worth asking
When a series changes its method, ask whether the publishing agency quantified the step, and then whether anyone drew the chart accordingly. Most series never get the first; this one did, and the number turned out to be small enough to be inconvenient for both of the easy stories about it. Ask also who a definition change makes visible, because the size of a break and the shape of it are separate questions with separate answers.
Source
Prevalence and Characteristics of Autism Spectrum Disorder Among Children Aged 8 Years - Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2018 — Maenner MJ, Shaw KA, Bakian AV, et al. (2021)
Read the source: https://doi.org/10.15585/mmwr.ss7011a1
DOI: 10.15585/mmwr.ss7011a1
How this was scored
- Study design
- not recorded
- Funding
- not recorded
- Published in
- not recorded
- Sample size
- not recorded
- Preregistered
- not recorded
- Conflicts disclosed
- not recorded
- Independent of proponent
- not recorded
- Retracted
- No
We have not finished checking this source, so there is no scoring to show yet. “We have not checked this yet” and “this is disputed” are different statements, so no scored band is shown rather than a low one.
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Published August 31, 2026.
Questions
How strong is the evidence behind this?
Resolv rates this source "not yet assessed". We have not finished checking this source. No judgement either way. One caveat travels with that badge: The bridge-study numbers cut against a tidy narrative in both directions, so both halves are printed here and neither may travel alone. The 2018 case-definition change is a genuine construct break, and the series must not be spliced across it. And the change's measured size - approximately no difference for 2014, 7% lower for 2016, with about 86% of children meeting both definitions - is far too small, and points the wrong way, to explain the 18.5 to 23.0 per 1,000 step it sits under. Quoting either half without the other misleads. One scope limit: the bridge analysis compares the two definitions on ADDM data for 2014 and 2016 only, and is not a general estimate of the change's effect in later surveillance years. The score is calculated from recorded facts about the source — study design, funding, publication venue, sample size, preregistration — not typed in by an editor.
What is the source for this?
Prevalence and Characteristics of Autism Spectrum Disorder Among Children Aged 8 Years - Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2018 — Maenner MJ, Shaw KA, Bakian AV, et al. (2021). DOI: 10.15585/mmwr.ss7011a1. The full source is linked on this page so you can read it yourself.
Is this medical advice?
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.