For a number of reasons, estimating the prevalence of autism spectrum disorder has been a challenging process.

Earlier this year, data from the Centers for Disease Control and Prevention (CDC) indicated that 1 in 59 children in the United States had autism in 2014. But now, a new government survey suggests that the current figure could actually be 1 in 40 children.

What is the reason for the discrepancy?

Michael Kogan, author of the new report, pointed out the lack of medical tests (like the examination of blood samples) to diagnose autism, which makes it "difficult to track," he said. To diagnose the disorder, a child will have to be screened by a pediatrician and have potential symptoms observed by experts. 

While the CDC report based estimates on 8-year-old children from 11 residential areas, the latest survey was much broader in scope, using more inclusive methods of data collection.

So which figure would be more accurate?

This is hard to determine as both findings have their fair share of limitations. Since the CDC was looking at 2014 estimates, one could say the 1-in-40 figure is a more accurate representation of current prevalence.

On the other hand, the new survey depended on parental reporting — which is not always clinically validated — and could be more prone to inaccuracies. Thomas Frazier, chief science officer of Autism Speaks, stated a preference for the CDC figures even if they might be "a bit conservative."

Based on the data, is autism on the rise?

While diagnoses are on the rise, experts have mixed opinions on whether the disorder is affecting more children than before due to some unknown trigger. 

For instance, we know that fewer babies are dying in the country than before, which means some of them may go on to be diagnosed with autism. Earlier this year, Daisy Christensen of the CDC also explained how the changing definition of autism could be a factor.

"Over the 80s and 90s, the diagnostic criteria expanded to include more children so I think that's definitely a possibility for the increase that we've seen," she said. Nevertheless, the authors of the latest report said more research was required to provide a firm answer to this question.

What other challenges are we facing?

Many parents who participated in the survey said they had trouble getting access to care for their children. Compared to the care needs of those with Down syndrome and other behavioral disorders, they were 44 percent more likely to have trouble accessing mental health care and 24 percent less likely to receive care coordination help.

"Though we've seen progress in recent years, this confirms what we know from our parents — that many children face unacceptable delays in getting a diagnostic evaluation, even after parents, teachers or other caregivers have recognized the signs of autism," Frazier said.