About 1 in 45 children in the United States has an autism spectrum disorder, according to a new government estimate of the condition's prevalence in 2014.

This new report is based on data collected during the yearly National Health Interview Survey, from interviews of parents about their children, and is the first report of the prevalence of autism in the U.S. to include data from the years 2011 to 2014, according to the researchers from the Centers for Disease Control and Prevention (CDC).

Although the new estimate looks like a significant increase from the CDC's previous estimate — which put the autism spectrum disorder rate at 1 in 68 children — the previous estimate was made using data from a different CDC survey, called the Autism and Developmental Disabilities Monitoring Network, which gathers information from children's medical records. This 1-in-68 estimate was reported in 2014, but was based on data collected during 2010.

None of the interview surveys and monitoring methods that report increasing prevalence rates of autism in the U.S. looked at why these numbers seem to be rising. But one reason could be that awareness of the condition has increased among both parents and health care providers, which has likely led to more children with the condition being identified, said Robert Fitzgerald, an epidemiologist in psychiatry at the Washington University School of Medicine in St. Louis, who was not involved in the research.

For example, in the past, some kids now considered to have an autism spectrum disorder (ASD) may have been labeled as having an "intellectual disability," he said. There have also been recent changes in the diagnostic criteria and symptoms used to describe ASD. [Beyond Vaccines: 5 Things That Might Really Cause Autism]

Another reason is that the stigma of having autism has decreased, Fitzgerald said. Previously, even doctors may not have wanted to give kids the label of "autism," leading children's medical records to reflect an underdiagnosis of actual cases. Now, there has been an increase in services and support for children who have ASD, so this may have resulted in a different mind-set, he said.

For the new report, nearly 12,000 parents of children ages 3 to 17 from across the U.S. sat down with researchers for face-to-face interviews in 2014, and about 11,000 parents were interviewed each year from 2011 to 2013.

The rate of autism in 2014 (1 in 45) was higher than the rate researchers found in 2011 to 2013, which was 1 in 80 children with ASD.

However, in 2014, the researchers changed the way they collected the data, said the lead author of the new report, Benjamin Zablotsky, an epidemiologist in the Division of Health Interview Statistics at the National Center for Health Statistics in Hyattsville, Maryland.

Therefore, much of what seems like an increase in ASD between 2011 and 2014 was actually a function of the way the interviewers asked the questions, Zablotsky said.

In 2014, the researchers first asked parents whether a doctor or health professional ever told them that their child had an intellectual disability, also known as mental retardation. The second question was a stand-alone question about ASD: Parents were asked whether a health professional ever told them their child had autism, Asperger's disorder, pervasive developmental disorder or autism spectrum disorder. The final question asked whether a health professional had ever told parents their child had any other developmental delay.

When interviewers questioned parents in 2011 through 2013, they asked the same first question about intellectual disability, but then their second question asked about other developmental delays. In the third question, parents were asked to look at a list of 10 conditions, including autism/ASD, and to indicate whether a health professional ever told them their child had one of these conditions.

This approach — of including autism in a checklist instead of asking a specific question about it — might have resulted in the name of the condition sometimes getting lost in the shuffle, Zablotsky said.

The revised approach was implemented in 2014 to better align with the wording used in other national surveys that estimate the prevalence of autism, and to include the specific terms that parents may have heard health care professionals use when making a diagnosis, Zablotsky said.

Also, putting the autism question second, before the question about other developmental delays, resulted in the 2014 data showing a higher prevalence rate for ASD, and a lower prevalence rate for other developmental delays. The opposite seemed to occur in 2011 to 2013, when the questions were the other way around — those data showed a higher reported rate of children with developmental delays, and a lower rate of ASD.

Increased prevalence

Fitzgerald agreed that what looks like an increase in autism's prevalence in 2014 was probably due to the way the interviewers asked the questions on the survey, rather than a real change in ASD prevalence within the population.

To see that big of a change in prevalence over a four-year period — from 1 in 80, to 1 in 45 — researchers would also need to be seeing a dramatic change in risk factors for autism in the population, Fitzgerald said. [9 Weird Ways Kids Can Get Hurt]

How parents understand and interpret the questions they are asked during an interview and how well they can accurately recall their child's diagnosis influence the responses they give and affects the results, Fitzgerald told Live Science.

The 2014 results were probably a more accurate measurement of the true prevalence of autism because they produced estimates similar to those of other recent survey methods, he said. The 2011-2013 data identified fewer cases of autism because of the way parents were answering the questions, he said.

The big question is whether the U.S. will continue to see an increase in cases of autism, Fitzgerald said.

Results from the last 10 years have been finding increases in prevalence rates, and they have not yet shown a leveling off, he said.

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