As ADHD and autism diagnoses rose, newly diagnosed children came to resemble their peers

Diagnoses of ADHD and autism have climbed steeply, and the argument over why rarely rests on evidence. A Danish registry study in JAMA Psychiatry offers a way to test one explanation: it asks whether the characteristics that mark out a diagnosed child from other children have changed as the diagnosed group grew [s1]. They have. Over a decade, the risk factors linked to a diagnosis weakened, meaning newly diagnosed children increasingly resembled their peers without a diagnosis — a pattern the authors read as changing diagnostic practice rather than a change in underlying risk [s1].

The study drew on nationwide Danish registries covering people born between 1994 and 2022, followed to age 18 [s1]. Children diagnosed with ADHD or autism spectrum disorder before 18, between 2012 and 2022, were treated as cases and each matched to 10 undiagnosed controls of the same sex, birth year, municipality and country of birth [s1]. Of 2,194,951 children and adolescents, 100,323 (4.6%) were diagnosed before 18; the 71,317 diagnosed in the 2012-to-2022 window (37.1% female; median age at diagnosis 11.4) formed the case group, matched with 713,170 controls [s1]. The researchers then tracked how 19 prediagnostic characteristics — family, perinatal and health-care factors — related to a later diagnosis, year by year [s1].

The signal: attenuation

Diagnosed children differed from controls on every characteristic, but those differences shrank over time, with the associations moving toward no effect, especially for socioeconomic and perinatal factors [s1]. The authors' worked example is low birth weight: its odds ratio for a later diagnosis fell from 1.54 (95% CI, 1.41 to 1.68) in 2012–2013 to 1.17 (95% CI, 1.10 to 1.24) in 2020–2022 [s1]. A risk factor that once separated diagnosed from undiagnosed children fairly sharply had, by the end of the decade, become a much weaker marker.

The weakening was uneven. It was greater for ADHD than for autism — for household income, the mean yearly change in the odds ratio was 6.5% (95% CI, 5.7% to 7.3%) for ADHD versus 0.7% (95% CI, −0.1% to 1.5%) for autism — and more pronounced among children diagnosed at ages 10 to 17 than among those diagnosed younger [s1]. The pattern was similar across sexes and held when the analysis was restricted to diagnoses made with higher certainty [s1].

What it does and does not mean

The authors' interpretation is careful, and worth quoting in spirit: that rising diagnostic rates "may reflect changes in diagnostic practices or health care capacity rather than changes in underlying risk alone," and — this is the part that is easy to misread — should "not be interpreted as evidence that ADHD or ASD have become less impairing at the individual level" [s1]. In plain terms: as services widened, the net caught children who look, on these background factors, more like the general population than earlier-diagnosed children did. That is consistent with better recognition of milder or less classically presenting cases. It is not evidence that today's diagnoses are less real, or that the children carrying them are less affected.

The design has the usual registry limits. These 19 characteristics are markers of association, not causes, and attenuation in Denmark's health system over one decade need not generalise to systems that diagnose differently. But the method sidesteps the usual dead end of prevalence debates, which argue over the rising count itself; here the finding is about who is being counted, and how that has shifted. It complements other registry work on ascertainment, such as the narrowing male-to-female ratio in autism and rising stimulant prescribing for ADHD.

Sources

• [s1] Changes in Characteristics Associated With ADHD and ASD Diagnoses Over Time, JAMA Psychiatry, 9 September 2026.