Even as autism prevalence has increased, new research finds that the likelihood of getting diagnosed with the developmental disorder remains largely tied to socioeconomics.

Children from lower income neighborhoods are less likely than those from wealthier backgrounds to be diagnosed with autism, according to findings published online this month in the American Journal of Public Health.

The study looked at data on 1.3 million 8-year-olds in 11 states that was collected between 2002 and 2010 through the U.S. Centers for Disease Control and Prevention’s Autism and Developmental Disabilities Monitoring Network.

Researchers cross-referenced this information with data from the U.S. Census Bureau on poverty, median household income and educational attainment, among other factors.

No matter what metric was used, the findings indicated that lower socioeconomic status was consistently tied to a reduced odds for autism. That held true even as prevalence of the developmental disorder more than doubled during the eight-year period studied.

“We wanted to see if part of this increase in ASD prevalence was because advances in screening techniques and medical training meant more children from disadvantaged backgrounds were gaining access to ASD diagnoses and services,” said Maureen Durkin of the University of Wisconsin-Madison’s Waisman Center who led the study. “It doesn’t seem that’s the case.”

Similar studies looking at Sweden and France, which both have universal health care, have found no association between the odds of autism and socioeconomic background, the researchers noted.

“If we are under-identifying ASD in certain socioeconomic groups — as seems likely — we need to be prepared to provide services at a higher level to more people,” Durkin said. “We need to find cost-effective interventions and supports and make sure they are distributed equitably and in a way that reaches everybody who needs them.”