Autism affects 1 in 91 children in the United States, government data published Monday shows, marking a dramatic increase over the previous estimate of 1 in 150.

The research published in the journal Pediatrics comes from a 2007 telephone survey of over 78,000 parents who were asked if they had ever been told by a health care provider that their child had an autism spectrum disorder.

Results from the survey show about 673,000 children diagnosed with autism, bringing the rate to 1 in 91 children, according to researchers from the Centers for Disease Control and Prevention and the Health Resources and Services Administration who jointly conducted the survey.

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Of parents who said their child had been diagnosed with autism, half indicated their child’s condition was “mild” while one third called it “moderate.” The remaining parents indicated that their child had a “severe” case.

In about 38 percent of cases parents reported that their child no longer had the diagnosis.

The 2007 survey marked the first time since 2002 that the government attempted to estimate the prevalence of autism, which many suspect to be on the rise. The 2002 measurement looked at data on 8-year-olds and concluded that autism occurred in 1 in 150 children.

While the significant increase in the rate of autism does appear to suggest a rise in the disorder, researchers say several factors could be at play. Greater public awareness and identification of autism and the inclusion of Asperger’s syndrome, pervasive developmental disorder and other autism spectrum disorders in the 2007 survey could contribute to the higher rate of diagnosis, they say. What’s more, the shear fact that children are being diagnosed with autism at younger ages than in the past means that more children would likely have an autism diagnosis at any one time.

Of children who once had an autism diagnosis but no longer did, many retained other similar diagnoses such as attention-deficit hyperactivity disorder or behavioral problems. Researchers say the difficulty in identifying autism especially in very young children could be the reason nearly 40 percent of children diagnosed with autism lose the diagnosis as they age.

Alternatively, some children could have received an autism diagnosis early on primarily to access needed early intervention or special education services. And, researchers also say the accuracy of parent reporting could be at issue.

The 2007 survey indicates that boys were four times more likely than girls to be diagnosed with autism. White children were also more likely to have the disorder than black or multiracial children. Furthermore, children living in the Northeast and Midwest had higher odds of having autism while children with less educated parents had lower odds.