A group of researchers from the Centers for Disease Control and Prevention published the first estimate of the prevalence of autism among adults in the United States, setting that rate at 2.21% or 1 in 45.
The research paper (PDF) also estimated prevalence from state-to-state, providing a valuable benchmark for states wondering what kind of resources and funding they should devote to supporting adults with autism. But the study’s authors acknowledged it had several limitations, and the value of its estimates has since been called into question.
The study, published in the Journal of Autism and Developmental Disorders, found the 2.21% rate of U.S. adults slightly higher than the 1.85% rate the CDC had most recently observed in U.S. children. The adult prevalence rate ranged from a low of 1.97% in Louisiana to a high of 2.42% in Massachusetts.
Thomas W. Frazier, the chief science officer for the group Autism Speaks, said the study "helps fill a critical gap in knowledge."
"With this knowledge, all of us in the autism community can be better equipped to figure out the programs and services that communities need to support autistic adults," Frazier said. "The data can also help states understand the specific needs of their communities and allow us to better provide for the roughly one-third of autistic adults – about 2 million people – who may need significant support beyond their childhood years."
But even the study’s authors said there were limitations to how confident they could be in their estimates. They arrived at their 2.21% figure not by studying adults with autism, but by extrapolating existing data on the prevalence of autism in U.S. children.
The authors noted that the data they used came from parents who reported that their kids had an autism diagnosis. Thus, it would exclude people who weren’t diagnosed by age 17, or erroneously include people whose parents were mistaken.
Their analysis also relied on the assumption that the prevalence of autism seen today in children was roughly the same in children of the past, which does not account for the possibility of environmental changes that could have altered prevalence over time. They also wrote that only a few such environmental factors have been identified, and none are believed to drastically alter the autism prevalence rate.
A study in England that relied on actually surveying adults, rather than extrapolating childhood data, found a much lower autism prevalence rate: just under 1%.
Jill Escher, the president of the National Council on Severe Autism, wrote that the CDC study’s authors "had some noble intentions," but strongly criticized their methodology and called the study’s conclusions "worse than useless."
"We desperately need policymakers to understand the prevalence and number of cases so we can support the legions of disabled adults," Escher wrote. "But this study offers nothing of value, and, worse, signals an alarming level of apathy about (the) causation of very serious neuro-developmental pathology that has flooded our communities."
The study’s results still provide a benchmark for businesses trying to determine how many of their employees or customers might benefit from accommodations for people with autism (PDF), such as limiting sensory over stimulation (PDF) and providing structure through things like written agendas for meetings.
But the concerns about the study’s reliability cast some doubt on how useful it will be for guiding state and federal funding of autism support programs, which currently focus largely on children (PDF).
The Autistic Self Advocacy Network, the only major advocacy group run entirely by people who themselves have autism, has said that members of the autism community should have a seat at the table in designing future research projects.
"Researchers and the autistic community can work together to help make our lives better," the group says.