This population-based matched case-control study used Danish nationwide registry data (births 1994–2022) to examine whether associations between 19 prediagnostic characteristics (socioeconomic, perinatal, health care use) and ADHD/ASD diagnoses changed from 2012 to 2022 in individuals followed to age 18.
Among 71,317 cases (ADHD or ASD) matched to 713,170 controls, associations between known risk factors and diagnosis weakened significantly over time. For example, the OR for low birth weight fell from 1.54 (95% CI, 1.41–1.68) in 2012–2013 to 1.17 (95% CI, 1.10–1.24) in 2020–2022. Attenuation was stronger for ADHD than ASD (mean yearly OR change: 6.5% vs. 0.7% for household income) and more pronounced in those diagnosed at ages 10–17 than at younger ages.
- Registry-based design captures diagnoses as recorded in Danish health systems, which may not reflect true prevalence or diagnostic accuracy. - Findings are from Denmark and may not generalize to other health care systems with different diagnostic practices. - The study cannot distinguish between changes in diagnostic thresholds, clinician behavior, and genuine shifts in population risk.
Rising ADHD and ASD diagnosis rates likely reflect broadening diagnostic practices or expanded health care capacity, not a true increase in underlying risk — but clinicians should not interpret this as evidence that these conditions are less impairing at the individual level. Children newly diagnosed, especially older adolescents, may have milder or less classically risk-burdened presentations than those diagnosed a decade ago.
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