Donald Trump said that autism cases are on the rise, but evidence suggests that's not true.

This is a common talking point of the anti-vaccine movement.

Trump has expressed opposition to vaccines in the past.

President Donald Trump told a roomful of teachers on February 14 that there's been a "tremendous amount of increase" in autism.

The president made the remarks during a listening session with parents, teachers and education secretary Betsy DeVos.

"So what's going on with autism?" Trump said after a principal at the meeting told him she worked at a special education center in Virginia that serves children with autism.

"When you look at the tremendous increase, it's really, it's such an incredible, it's really a horrible thing to watch the tremendous amount of increase," the president said. "Do you have any idea? And you're seeing it in the schools."

When the principal told him that one in sixty-eight children has autism, Trump again suggested the number was on the rise, adding "Well, maybe we can do something about that."

Experts on autism, however, haven't found evidence that incidence of the condition is increasing.

New York Magazine's Jesse Singal, who first highlighted the president's claim, interviewed autism expert and NeuroTribes author Steve Silberman about the remarks. Here's the key excerpt:

“There’s no consensus as to whether or not there’s been any significant increase in the actual prevalence of autism, period,” says Silberman. “The real debate is whether or not there has been a small increase, and there are a number of factors that could play a role in that small increase. For instance, it’s well established that older parents have more autistic kids and people are waiting longer to get married and have kids now... But the consensus is that there has been no huge, startling, ‘horrible,’ as Trump said, increase in autism. And the CDC estimate has been flat for a couple of years... because the major source of the increase that started in the 1990s was broadened diagnostic criteria and much more public awareness of what autism looks like.”

In other words, there may be a few cultural changes that make autism rates fluctuate slightly over time, but the gradual increase in diagnoses can most likely be attributed to researchers getting better at spotting autism, rather than more people having autism.

Other autism experts agree with Silberman. The genticist Santhosh Girirajan found in 2015 that the increase in autism diagnoses matches a general decline in more generic "intellectual disability" cases — suggesting kids are just being shifted from one category to another.

Autism as it's understood today is in fact a fairly new diagnosis. As recently as the 60s and 70s, some researchers falsely thought the disease was caused by "refrigerator mothers" who didn't love their children enough. Autism wasn't understood as a genetic issue until the 1980s, and schools only began treating autism as a special education category in the 1990s.

There's a good chance you've met someone in their 60s, 70s, or 80s who might have been diagnosed with autism if they'd been born today, but were just seen as exhibiting unusual behavior in their childhood.

The notion that autism is on the rise is a talking point of the anti-vaccine movement — a group that believes parents shouldn't vaccinate their kids based on research from a fraudulent 1998 study.

Trump has referenced anti-vaxxer claims before. Here's a tweet from 2014:

More recently, Trump met with Robert Kennedy Jr., an anti-vaccine activist who has published books about the alleged dangers of the treatment. He claims (without scientific evidence) that a cabal of scientists are poisoning children for profit by giving them vaccines. After his meeting with Donald Trump, Kennedy reportedly thought he'd be selected to chair a presidential panel on" vaccine safety and scientific integrity."

Andrew Wakefield, the author of the fraudulent 1998 study, also attended Trump's inaugural ball.

The recent opposition to vaccines has caused concern among scientists and medical professionals, since there's evidence that the movement has led to a measurable spike in measles outbreaks in the US. Measles can be fatal to children, as can pertussis and other ailments that vaccines prevent.

The estimated number of lives saved by childhood vaccinations measures in the hundreds of thousands.

Here's the video of the president's exchange: