The changing prevalence of autism in California.
Level 3 - non-randomized controlled study
Retrospective population-based birth cohort study
PubMed 12108622 · doi:10.1023/a:1015453830880
What was done
Researchers analyzed eight successive California birth cohorts (1987–1994, totaling 4,590,333 births) using data from the statewide agency responsible for coordinating services for developmental disabilities. They identified children with full syndrome autism to evaluate prevalence changes alongside maternal age, race/ethnicity, maternal education, child gender, and plurality. They also evaluated trends in mental retardation without autism to test for diagnostic substitution.
What was found
A total of 5,038 children had full syndrome autism (overall prevalence of 11.0 per 10,000). From 1987 to 1994, autism prevalence increased from 5.8 to 14.9 per 10,000 (absolute increase of 9.1 per 10,000), independent of maternal age, race/ethnicity, education, gender, or plurality. During the identical period, prevalence of mental retardation without autism decreased from 28.8 to 19.5 per 10,000 (absolute decrease of 9.3 per 10,000).
Why it matters
This study provides evidence that improvements in detection and diagnostic substitution away from mental retardation largely account for observed increases in autism prevalence in California.
Limits
The study relied on administrative records rather than direct clinical diagnostic assessments. It could not determine whether an underlying true increase in incidence also occurred.
Cited by
- context Autism prevalence in children has increased from 1 in 10,000 to approximately 1 in 130 over recent decades.