A substantial number of children who meet the criteria for autism are failing to receive a formal diagnosis, according to a new study based on data from the Centers for Disease Control and Prevention.

The study published late last month in the journal Autism Research found that 25 percent of those on the spectrum have no diagnosis and these overlooked children are most likely to be black or Hispanic.

Researchers analyzed data collected through the CDC’s Autism and Developmental Disabilities Monitoring Network on 266,000 children in 11 states who were 8-years-old in 2014. Educational and medical records for each child were evaluated to determine if they qualified for an autism diagnosis.

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The study found that nearly 4,500 of the children were on the autism spectrum, but a quarter of these kids had no official diagnosis.

“There may be various reasons for the disparity, from communication or cultural barriers between minority parents and physicians to anxiety about the complicated diagnostic process and fear of stigma,” said Walter Zahorodny, an associate professor at Rutgers New Jersey Medical School and one of the study authors. “Also, many parents whose children are diagnosed later often attribute their first concerns to a behavioral or medical issue rather than a developmental problem.”

Most of the kids without a diagnosis were boys without intellectual disability who generally needed fewer supports than those with a diagnosis, the study found.

Researchers said it’s important that all children be properly diagnosed so that they can receive treatment tailored to their needs. The study authors said better screening and other steps are needed to reduce disparities.