Trends in the Prevalence of Autism Spectrum Disorder in California: Disparities by Sociodemographic Factors and Region Between 1990-2018.
Karl O'Sharkey, Sanjali Mitra, Seung-A Paik and 3 others
PMID 38700778WHAT IT FOUND
Autism diagnosis rates in California have shifted from affluent, White communities to lower-income, Hispanic and Black communities.
Girls are now diagnosed at a ratio closer to 3:1 with boys. Clinicians should expect rising referrals from underserved regions and younger patients presenting with later-diagnosed profiles.
Key findings
01ASD cumulative incidence rose sharply from 1990 to 2018, with the highest rates now found in lower socioeconomic status neighborhoods and among Hispanic and Black children, reversing earlier trends.
02The ratio of boys to girls diagnosed with ASD narrowed from approximately 5:1 in the early 1990s to closer to 3:1 by 2018, suggesting improved identification of girls.
03Average age at diagnosis decreased over the study period, but significant regional disparities remain, with some high-incidence areas like the San Joaquin Valley still experiencing delayed diagnoses compared to metropolitan regions.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTsWhat it means for SLPs
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What it does not show
The study relies on DDS records, which capture only about 75-80% of all children with ASD in California, potentially underestimating true prevalence. DDS data may skew towards more severe cases in some regions, biasing comparisons. Changes in diagnostic criteria (DSM-IV to DSM-5) and increased awareness over the 30-year period make it difficult to separate true incidence changes from diagnostic artifacts. The denominator includes all live births, regardless of whether children died or moved out of state, which may underestimate incidence. Small cell counts prevented further breakdown of Asian and Pacific Islander subgroups.
Declared interests
The study was funded by the California Air Resources Board. No other conflicts of interest were declared in the provided text.
The easy way to misread this
Do not interpret the rising incidence rates as evidence that autism is biologically more common in these specific demographic groups today. The trends likely reflect increased access to diagnosis and reduced barriers for minority and lower-income populations, rather than a change in the underlying condition's prevalence.