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A government survey of parents says 1 in 50 U.S. schoolchildren has autism, surpassing another federal estimate for the disorder — but that doesn't necessarily mean Utah's previous high rate is actually even higher.

Health officials say the new number doesn't mean autism is occurring more often. But it does suggest that doctors are diagnosing autism more frequently, especially in children with milder problems.

The earlier government estimate of 1 in 88 comes from a study that many consider more rigorous. It looks at medical and school records instead of relying on parents, and involved 14 states, including Utah.

What the new numbers mean for Utah — where rates of autism spectrum disorder are among the highest in the nation and nearly double the national average — isn't entirely clear.

"We won't know until our 2010 study is finished," said Judith Pinborough-Zimmerman, a research assistant professor in the University of Utah's Department of Psychiatry and a lead investigator for the 14-state study.

For decades, autism meant kids with severe language, intellectual and social impairments and unusual, repetitious behaviors. But the definition has gradually expanded and now includes milder, related conditions.

The new estimate released Wednesday by the Centers for Disease Control and Prevention would mean at least 1 million children have autism.

The number is important — government officials look at how common each illness or disorder is when weighing how to spend limited public health funds.

It's also controversial.

The new statistic comes from a national phone survey of more than 95,000 parents in 2011 and 2012. Less than a quarter of the parents contacted agreed to answer questions, and it's likely that those with autistic kids were more interested than other parents in participating in a survey on children's health, CDC officials said.

Still, CDC officials believe the survey provides a valid snapshot of how many families are affected by autism, said Stephen Blumberg, the CDC report's lead author.

Zimmerman agrees and believes the survey validates CDC's earlier estimate for Utah, rather than suggesting the state's already-high rates are higher. "At the present time the best estimate [for prevalence] we have is around 1 in 47," she said.

That earlier study had its own limitations. It focused on 14 states, only on children 8 years old, and the data came from 2008. Updated figures based on medical and school records are expected next year.

But it yielded a higher estimate for Utah than a conservative state Department of Health study released in January showing 1 in 63 Utah children to be at risk for autism.

"We've been underestimating" how common autism is, said Michael Rosanoff of Autism Speaks, an advocacy group. He believes the figure is at least 1 in 50.

There are no blood or biological tests for autism, so diagnosis is not an exact science. It's identified by making judgments about a child's behavior.

Doctors have been looking for autism at younger and younger ages, and experts have tended to believe most diagnoses are made in children by age 8.

However, the new study found significant proportions of children were diagnosed at older ages.

Roula Choueiri, a neurodevelopmental pediatrician at Tufts Medical Center in Boston, said she's seen that happening at her clinic. Those kids "tend to be the mild ones, who may have had some speech delays, some social difficulties," she wrote in an email. But they have more problems as school becomes more demanding and social situations grow more complex, she added.

Tribune reporter Kirsten Stewart contributed to this story. —

Autism in Utah

Conservative state Department of Health estimates show 1 in 63 Utah children is at risk for an autism spectrum disorder. A recent study just released by the CDC suggests the risk may be even higher, validating earlier findings pegging Utah's rate at 1 in 47.

Utah rates of autism spectrum disorder are among the highest in the nation and nearly double the national average.

Utah boys are nearly four times more likely than girls to be diagnosed.

Reasons for increases in the rate are unknown but may be related to: improvements in screening, diagnosis, and treatment; greater awareness of the condition; and/or improved documentation.

Source: Utah Department of Health