The Centers for Disease Control and Prevention said Wednesday that a recent survey of parents shows that 1 in 50 U.S. schoolchildren has some form of autism. According to the Associated Press, the higher numbers don't mean that cases of autism are occurring more often, but rather that tests to detect it have become more precise and that doctors are diagnosing it more often.

The new number could mean that as many as one million children in the U.S. have autism and would affect how public health and education funds are spent, but the numbers do not come without controversy.

An earlier study, one that looked at medical records and school reports and determined that 1 in 88 children is struggling with the disorder, which can contribute to developmental, intellectual and linguistic impairments as well as difficulties with social interaction and, in severe cases, can give rise to unusual, repetitive behaviors. Many medical experts maintain that the earlier study is more accurate because it did not rely solely on parental testimony.

The CDC survey released Wednesday was a telephone poll of 95,000 parents in 2011 and 2012. Less than one quarter of families contacted agreed to take the survey and critics suggest that parents of children with autism or related disorders like Asperger's Syndrome would be more likely to participate in a survey about child development.

Study author Stephen Blumberg of the CDC conceded that may be so, but said that the study is a crucial window on how many U.S. families are being affected by the disorder.

The AP suggested that the earlier, 1 in 88 study had limitations of its own. It only sampled children in 7 states, only children 8 years old and the data is now five years old, coming from 2008.

"We've been underestimating," said Michael Rosanoff of the advocacy organization Autism Speaks. He believes the 1 in 50 number is much closer to reality.

Autism is still little understood. There are no blood or other physiological tests that can determine whether a child has it. Its causes are unknown. Thousands of families in the U.S. and beyond have foregone vaccinations for their children mistakenly believing that the injections contain contaminants that cause autism.

One other contributor in the diagnostic increase is that children are being diagnosed not just at younger ages, but older ones as well. Dr. Roula Choueiri, a neurodevelopmental pediatrician at Tufts Medical Center in Boston, told the AP that she has seen this at her clinic. Children diagnosed at older ages "tend to be the mild ones, who may have had some speech delays, some social difficulties."

Typically children are diagnosed at around 8 years of age, but closer study is finding that some children develop symptoms later, as school and social interactions become more stressful and complex.

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