Hey, I'm Flora Lichtenen, and you're listening to Science Friday.

There's a long-held idea that autism is more prevalent in boys than girls, like three times more common, according to the CDC.

But a growing body of research suggests the story is more complicated. In a new study, researchers

tracked autism diagnoses in millions of Swedish people born from 1985 to 2022. And here's what they

found. The prevalence of autism is actually pretty even across the sexes, but people with

female stamped on their birth certificate are often diagnosed later in

life. The study tracked sex assigned at birth, which is why you'll hear us use that language.

Here to give us a rundown on the study is epidemiologist Dr. Caroline Fife, the lead author who did

the research at the Karolinska Institute in Sweden. Caroline, thanks for being here. Thank you.

What made you want to look into this?

So we have been looking at sex differences in autism and we wanted to look at the influence of time scale because what we had noticed was that over time autism diagnosis had increased

markedly, but the sex difference seemed to remain

at about three to one. And so we were interested in why that was occurring and whether that had

something to do with either the age, children were diagnosed, the period in time at which they were diagnosed, or was it something to do with each generation, so the birth cohort.

And what did you find?

What we found was that the sex difference hadn't changed in children under 10 over that time.

It fluctuated between about 2.5 and 4 boys for every girl

diagnosed, but it hadn't actually changed. But when we looked at children over the age of 10

and adults, the sex difference had gone down markedly over that same period. And in particular,

we found that there was an increase in the

number of girls diagnosed during adolescence. Wow. So the diagnoses catch up for girls as they get

older. Exactly so. So the average age overall is 10 to 14 for boys and it's 15 to 19 for girls.

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