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.