One in 45 U.S. children have autism, according to new government figures.

The latest estimate released on Friday is a significant leap up from the 2011 figure - one in 80 - and the currently held estimate of one in 68.

Experts warn the new data is largely the result of a change in the way the Centers for Disease Control and Prevention collects information on autism.

However, advocacy groups say the new number supports a belief that one in 68 is an underestimate.

The CDC runs three different surveys a year to generate various estimates. The most rigorous one gives the lower estimate of one in 68 children.  

The new number is from a survey of parents of 13,000 children, who were asked last year if their child were ever diagnosed with autism or a related disorder. 

The lower CDC estimate is from researchers checking health and school records for more than 47,000 children.

The one in 68 will still be treated as the best estimate, said Michael Rosanoff, director of public health research for the advocacy group Autism Speaks.

But he welcomes the new number as a suggestion that one in 68 is an underestimate, he added.

Estimates of how common autism is have been steadily increasing. In 2007, the CDC estimated 1 in 150 children had autism.

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 cause or causes of autism are still not known.

Experts say teachers and parents are increasingly likely to say a child with learning and behavior problems is autistic, so at least some of the apparent increase is due to different labeling.