Rates of autism spectrum disorder among children in the U.S. remained stable from 2014 to 2016, according to new research—a change from previous studies that found steady increases over the past two decades.
The new research letter, published in JAMA, looked at survey responses from a nationally representative sample of more than 30,000 children, ages 3 to 17, and their families. From 2014 to 2016, adults in each household were asked if a doctor had ever told them that their child had autism, Asperger’s disorder, pervasive developmental disorder or autism spectrum disorder. Data from the study was then adjusted to account for differences in people’s age, gender and ethnicity.
The researchers found that in 2014, 2.24% of participating children were reported to have an autism spectrum disorder. That number rose only slightly in 2015 and 2016, to 2.41% and 2.58%, respectively—an increase that was not statistically significant.
Autism rates did vary by sub-group. Over the three-year period, 3.54% of boys were reported to have an autism spectrum disorder, compared to 1.22% of girls. Prevalence was 1.78% in Hispanic children, 2.36% in black children and 2.71% in white children.
The overall estimate for autism prevalence among children in the analysis—2.4%—is higher than another recent estimate, from the Autism and Developmental Disabilities Monitoring (ADDM) Network, of 1.46%. The discrepancy may be explained by differences in study design, the authors note in their report. For example, the new study asked parents if their child has received a diagnosis, while the previous study looked at education and health-care evaluations.
The current study did not gather information about possible causes for autism and how those factors may (or may not) have changed over time. And, although the survey the researchers used has been going on since the 1960s, the question about autism was changed in 2014—so it cannot be used to estimate change in autism prevalence rates during earlier years.
Several large studies have suggested that autism rates have risen steadily in the last 20 years, but this new report suggests that rates may be leveling off. The ADDM Network’s estimated rates also plateaued between 2010 and 2012 (after increasing roughly 123% between 2002 and 2010), but then jumped 30% from 2012 to 2014.
Changes in diagnostic criteria, an increase in public awareness and more children being referred to physicians have all been suggested as possible causes for the previously documented rise in autism rates, the authors wrote in their report. So have potential changes in genetic and environmental risk factors. “Continued monitoring of the prevalence and investigation of changes in risk factors are warranted,” they concluded.