Access to behavior therapists is woefully lacking in many places, with a new study finding that more than half of the nation’s counties don’t have a single one.

Even in communities with board-certified behavior analysts, or BCBAs, the number of providers available to serve each child with autism varies greatly, researchers found.

The findings come from a study published recently in the journal Autism that looked at all 3,108 counties in the 48 contiguous states and Washington, D.C.

Researchers cross-referenced information from the Behavior Analyst Certification Board’s registry of providers with data from the U.S. Census and the Department of Education’s Civil Rights Data Collection in an effort to estimate both the number of BCBAs and the prevalence of children with autism in each county.

They found that 1,667 counties had no BCBAs. Of those, 325 neighbored counties that also had none of the providers.

There were 784 counties considered to have the highest access to BCBAs, up to 17 children with autism per therapist. On the flip side, the 129 counties with the lowest access had more than 137 kids with the developmental disability per BCBA.

The study notes that the professional organization for BCBAs recommends that each therapist manage six to 12 clients at a time or 12 to 16 if they are supported by an assistant.

The locations with the greatest access to BCBAs tended to be wealthier and had fewer uninsured residents, the study found.

When the researchers examined the 129 counties with the highest prevalence of autism, they found that 55 of them had zero BCBAs. Nine of these counties also had no therapist in any neighboring counties.

“Importantly, the differences in BCBA distribution cannot be fully explained by the county-level variation of ASD prevalence, suggesting that demand for the treatment of ASD is not necessarily driving provider supply,” wrote researchers from the University of Pennsylvania and the University of Louisville in their findings.

They point to the location of training programs and varied reimbursement rates as factors that could be driving the availability of BCBAs in various areas, but said more research is needed to fully understand what’s behind the unequal distribution and how to address it.