The public may not realize it, but the Centers for Disease Control and Prevention has three different ways of estimating the prevalence of autism.
One of those is the National Health Interview Survey, and the latest such survey shows 2.24 percent of children -- or roughly one in 45 -- had autism in 2014, compared to 1.25 percent for the three years 2011, 2012, and 2013 combined.
CDC freely acknowledges, however, that the higher rate is to be taken with a grain of salt, given changes in the way the survey was worded and administered. In fact, the prevalence of autism, intellectual disability, and developmental disability as a group didn't rise, it said.
"The prevalence of having any of the three conditions was constant across survey years," according to National Health Statistics Reports, No. 87, dated Nov. 13.
Three factors may have influenced the results, CDC said. First, surveyors asked parents about autism directly, as a stand-alone question, rather than merely asking them to check a box on a list various conditions their children might have.
Second, the question was made more elaborate, specifically: ''Did a doctor or health professional ever tell you that [child's name] had autism, Asperger's disorder, pervasive developmental disorder, or autism spectrum disorder?''
Finally, the order of questions was changed, so that the question about autism came second. Previously, the checklist that included autism came third, after questions about intellectual disability and other developmental delays.
"It ... cannot be concluded that the increase seen in the prevalence of [autism spectrum disorder] is completely explained by the three changes made to the survey," the report said. "However, the virtually identical prevalence estimates of children ever diagnosed with any developmental disability in 2011-2013 and 2014 suggests that, before 2014, some parents of children diagnosed with ASD reported this developmental disability as other [developmental delay] instead of, or in addition to, ASD."
CDC's other survey methods are the Autism and Developmental Disabilities Monitoring Network, which covers 8-year-olds, and the National Survey of Children's Health, which covers children ages 6-17.
The NHIS covers children ages 3-17, with a survey size of 13,000, compared to 360,000 for the monitoring network and 95,000 for NSCH.
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One of those is the National Health Interview Survey, and the latest such survey shows 2.24 percent of children -- or roughly one in 45 -- had autism in 2014, compared to 1.25 percent for the three years 2011, 2012, and 2013 combined.
CDC freely acknowledges, however, that the higher rate is to be taken with a grain of salt, given changes in the way the survey was worded and administered. In fact, the prevalence of autism, intellectual disability, and developmental disability as a group didn't rise, it said.
"The prevalence of having any of the three conditions was constant across survey years," according to National Health Statistics Reports, No. 87, dated Nov. 13.
Three factors may have influenced the results, CDC said. First, surveyors asked parents about autism directly, as a stand-alone question, rather than merely asking them to check a box on a list various conditions their children might have.
Second, the question was made more elaborate, specifically: ''Did a doctor or health professional ever tell you that [child's name] had autism, Asperger's disorder, pervasive developmental disorder, or autism spectrum disorder?''
Finally, the order of questions was changed, so that the question about autism came second. Previously, the checklist that included autism came third, after questions about intellectual disability and other developmental delays.
"It ... cannot be concluded that the increase seen in the prevalence of [autism spectrum disorder] is completely explained by the three changes made to the survey," the report said. "However, the virtually identical prevalence estimates of children ever diagnosed with any developmental disability in 2011-2013 and 2014 suggests that, before 2014, some parents of children diagnosed with ASD reported this developmental disability as other [developmental delay] instead of, or in addition to, ASD."
CDC's other survey methods are the Autism and Developmental Disabilities Monitoring Network, which covers 8-year-olds, and the National Survey of Children's Health, which covers children ages 6-17.
The NHIS covers children ages 3-17, with a survey size of 13,000, compared to 360,000 for the monitoring network and 95,000 for NSCH.
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