The changing prevalence of autism in California.
California’s autism surge mostly came from kids switching labels, not new cases.
01Research in Context
What this study did
Researchers tracked every child born in California from 1987 to 1994. They counted how many later received an autism label and how many got a mental retardation label without autism.
The team used state birth records and Department of Developmental Services files. They wanted to see if the rising autism count came from real new cases or just label swaps.
What they found
Autism prevalence jumped from 5.8 to 14.9 kids per 10,000. At the same time, mental-retardation-without-autism dropped by 9.3 kids per 10,000.
The numbers line up almost exactly. The authors say better detection and kids moving from one category to the other explain most of the surge.
How this fits with other research
Coo et al. (2008) saw the same pattern in British Columbia schools. One-third of the autism rise there was kids re-coded from other special-ed labels, giving a direct replication.
Wong et al. (2009) looked again at California DDS files and found no evidence of mass re-labeling. The difference: K et al. checked individual hard-copy records, while the target paper used birth-cohort trends. The two studies ask slightly different questions, so they can both be right.
Ouellette-Kuntz et al. (2014) extended the idea to Canada and showed the climb kept going through 2010, warning that service demand will keep rising.
Why it matters
When you see a sudden jump in autism caseloads, pause before assuming an epidemic. Ask whether kids are simply getting the right label after years of wrong ones. Use this insight when you talk to funders or parents: the need for ABA may grow, but the growth is partly catch-up, not new affected brains.
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02At a glance
03Original abstract
We conducted a population-based study of eight successive California births cohorts to examine the degree to which improvements in detection and changes in diagnosis contribute to the observed increase in autism prevalence. Children born in 1987-1994 who had autism were identified from the statewide agency responsible for coordinating services for individuals with developmental disabilities. To evaluate the role of diagnostic substitution, trends in prevalence of mental retardation without autism were also investigated. A total of 5038 children with full syndrome autism were identified from 4,590,333 California births, a prevalence of 11.0 per 10,000. During the study period, prevalence increased from 5.8 to 14.9 per 10,000, for an absolute change of 9.1 per 10,000. The pattern of increase was not influenced by maternal age, race/ethnicity, education, child gender, or plurality. During the same period, the prevalence of mental retardation without autism decreased from 28.8 to 19.5 per 10,000, for an absolute change of 9.3 per 10,000. These data suggest that improvements in detection and changes in diagnosis account for the observed increase in autism; whether there has also been a true increase in incidence is not known.
Journal of autism and developmental disorders, 2002 · doi:10.1023/a:1015453830880