Rates of autism among American children nearly doubled in 2014, according to a new analysis by the Centers for Disease Control and Prevention.

According to the new CDC survey of U.S. parents, the incidence of Autism Spectrum Disorder (ASD) in kid’s ages 3 to 17 years jumped from 1.25 percent between 2011 and 2013 to 2.24 percent in 2014, the Wall Street Journal reports.

But researchers noted a small tweak in the way the 2014 survey was conducted may be responsible for the staggering new figures.

In 2014, the CDC changed the method of assessing prevalence of autism in children based on their parents’ reports. In a 2011-2013 survey, parents had to answer three questions — whether their children were intellectually disabled, whether they noticed a developmental delay, and whether kids were previously diagnosed with Down syndrome, cell anemia, or other conditions.

A year later, CDC researchers asked directly whether the kids were diagnosed with ASD prior to the survey. About 10,000 parents take part in the CDC surveys every year.