A government survey of parents in the U.S. says 1 in 50 schoolchildren has autism. That surpasses another federal estimate for the disorder.

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

The earlier government survey estimated 1 in 88 U.S. schoolchildren has autism. It looked at medical and school records. The latest survey interviewed more than 95,000 parents in 2011 and 2012.

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.

Michael Rosanoff of the advocacy group Autism Speaks, says, "We've been underestimating" how common autism is.

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