Autism Rates Appear To Be Even Across Sexes. Diagnosis Is Not

FLORA LICHTMAN: Hey, I’m Flora Lichtman. 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 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 Fyfe, the lead author who did the research at the Karolinska Institute in Sweden. Caroline, thanks for being here.

CAROLINE FYFE: Thank you.

FLORA LICHTMAN: What made you want to look into this?

CAROLINE FYFE: 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.

FLORA LICHTMAN: And what did you find?

CAROLINE FYFE: What we found was that the sex difference hadn’t changed in children under 10 over that time because 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.

FLORA LICHTMAN: Wow. So the diagnoses catch up for girls–

CAROLINE FYFE: Exactly so.

FLORA LICHTMAN: –as they get older.

CAROLINE FYFE: Exactly so. So the average age overall is 10 to 14 for boys, and it’s 15 to 19 for girls. You start to see girls catching up, and particularly later adolescents, between the ages of 15 to 19. You see this rapid catch-up. By the age of 20, it was 1 to 1. So there was as many boys as girls diagnosed.

FLORA LICHTMAN: We know that research suggests that autistic people are more likely to be trans. Were you able to account for trans people or non-binary people in this study?

CAROLINE FYFE: No, we weren’t. There’s potential in Swedish registers to do that, so that is something that could happen in the future. But we didn’t do it for this study.

FLORA LICHTMAN: You’re not a clinician, and your focus is on the epidemiology. But from your point of view, does this study suggest that diagnostic criteria needs to change or that we need to understand autism differently? What flags does it raise for you?

CAROLINE FYFE: I think it does raise flags about the diagnostic criteria, because boys have always been diagnosed with autism at higher rates than girls. The research has been done mainly on boys, including all aspects of it, so the genetics, as well as the behavioral. And that may have influenced how these criteria were developed and how they’re interpreted towards a male-focused view on autism. So perhaps a good idea would be to try and extend that to understand more about how autism manifests in girls.

FLORA LICHTMAN: I mean, medical sexism– tale as old as time.

CAROLINE FYFE: [CHUCKLES] Indeed.

FLORA LICHTMAN: [LAUGHS] Dr. Caroline Fyfe is an epidemiologist and the lead author on this study. She did the research at the Karolinska Institute in Sweden. Caroline, thanks for being with us.

CAROLINE FYFE: Thank you very much for having me.

FLORA LICHTMAN: This study brings up a lot of questions, like what accounts for this discrepancy in the timing of diagnoses? And how does a missed or late diagnosis play out for people? A warning that the answers can get heavy. Dr. Rachel Moseley is a researcher in psychology at Bournemouth University in the UK who studies the experiences of autistic adults, especially women. And she’s the perfect person to give us insight because not only does she study this, she’s lived it herself. She was diagnosed as autistic in her late 20s. Rachel, welcome to Science Friday.

RACHEL MOSELEY: Oh, thank you so much for having me here.

FLORA LICHTMAN: What do you make of this study we were just talking about?

RACHEL MOSELEY: It’s wonderful to see because it confirms something that autism researchers, and of course, autistic people, have known for a very long time, and that is that autism is markedly underdiagnosed in people assigned female at birth. So we’ve known that for a number of years. And there have been other studies that really back this up. But it’s taken such a long time for that message to go through. So it’s just great to see more and more evidence really showing us that, yes, women, girls, people assigned female at birth– they’re out there.

FLORA LICHTMAN: As we said earlier, autism is reported to be three times more common in boys than girls. Why has that been the prevailing wisdom?

RACHEL MOSELEY: Well, there’s a number of reasons. When autism ended up in the diagnostic manuals, it was based on these descriptions of male cases. So for instance, people would be diagnosed if they showed a very stereotypical presentation. They would have to have very delayed or absent language. They would have to have differences that were evident from very, very early on. And this flies in the face of what we now know about how autism presents in women, girls, people assigned female at birth.

FLORA LICHTMAN: Tell me more about that.

RACHEL MOSELEY: Yeah, we know that the difference between autistic boys and non-autistic boys is really obvious from early on, and it remains obvious throughout their childhood. What we see in girls, in contrast, is that autistic girls are much closer to their non-autistic peers in terms of the way they present their kind of outward social appearance. So they don’t seem very different in childhood. But what we see in girls is that the size of that difference grows. So by the time they’re in late childhood, early adolescence, the difference between them and their peers is much more stark.

FLORA LICHTMAN: Do we know why that’s the case?

RACHEL MOSELEY: One suggestion is that autistic girls, typically, they may be slightly better at masking their autism. You don’t know that you’re masking, necessarily. You just know that if you behave in a certain way, you are less likely to be bullied or rejected. What’s really important is if you look at their social understanding, they’ve got equal difficulties as autistic boys. But outwardly, they seem more proficient.

And the reason that things will start emerging more as children get older is that the social world is becoming increasingly more complicated. You’ve got puberty and hormones. You’ve got social relationships becoming a lot more complicated. So all things that put greater strain on autistic girls, and hence their differences start to stand out more.

FLORA LICHTMAN: I mean, besides symptoms showing up later, are the signs themselves or the symptoms themselves different?

RACHEL MOSELEY: Yes. Yes, they are. Their autism does often look slightly different. So for instance, they might use eye contact slightly more than men. Their friendships look more typical to non-autistic children. So they are more likely to be on the fringe of the social group, whereas autistic boys are more likely to be explicitly rejected. And their interests likewise seem to be a little bit different in the way they present than you see in males.

So you might have the little boy who is fascinated in different designs of tomato soup cans over the years, something like that, whereas in girls, what you’re more likely to see, interests that are relational. They are about people, programs, celebrities. It will mark out that they’re autistic, but doesn’t stand out. It just doesn’t line up with what people know or believe they know about autism. And hence the girls don’t get flagged up as developing differently.

FLORA LICHTMAN: Let’s put you in charge. If you were rewriting the diagnostics for autism, where would you begin?

RACHEL MOSELEY: Gosh, where do I start?

[LAUGHTER]

So I want to say that researchers, clinicians have already done a very good job at redesigning these diagnostic criteria. And they are massively improved to where they were before. So we now recognize masking, for instance. But I think one thing I would do, since you’re giving me a wonderful power here where I can redesign this, I think it’s so important that the diagnostic criteria are updated to reflect what we now know about neurodiversity.

So the way we diagnose autism and the way we tell someone about their autism really matters. And of course, the diagnostic criteria now are all about symptoms. They’re all about disorder. And we know that if we use a strengths-based approach, and we explain more about difference, and these are the strengths you have as an autistic person, yeah, you do have these areas of challenge, but you have these strengths as well. And everyone has areas of challenge. There are things that autistic people are better at than non-autistic people. So I would like to redesign those diagnostic criterias to be much more neurodiversity-affirmative.

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FLORA LICHTMAN: Yeah, well, that is the perfect segue, Rachel, because coming up after the break, we’re going to ask you about how late and misdiagnoses affect people’s lives.

RACHEL MOSELEY: Yeah.

FLORA LICHTMAN: Does that sound OK?

RACHEL MOSELEY: Absolutely.

FLORA LICHTMAN: OK. Don’t go away.

RACHEL MOSELEY: [CHUCKLES]

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FLORA LICHTMAN: All right, let’s dive in. So how does being diagnosed later in life with autism, or not being diagnosed at all, what is the effect on people?

RACHEL MOSELEY: [SIGHS] I’d say, across studies, research is showing us that being missed for diagnosis has a profoundly negative impact on people. So the people I typically hear from in my research and that other studies document, people who grow up undiagnosed, they grow up knowing they’re different in some way. You know you’re different, but you don’t have an explanation for it.

You struggle at school. You struggle in relationships. You struggle in employment. You struggle across your life. You’re vulnerable to exploitation, abuse. You have complex, treatment-resistant physical and mental illness. But you don’t have an explanation for any of this, apart from the fact that you have to find an explanation. So it’s you. You’re stupid or weak or broken or weird. So you blame yourself, and other people blame you for being different and not being able to do what everyone else can do.

And really, really, sadly, we find that being missed for diagnosis, or being late diagnosed, is associated with higher suicide rates. So autistic people themselves link being missed for diagnosis with their suicidality. And in fact, they actually identify that improving diagnosis, and particularly picking up autism in girls and women, is a way to prevent suicide.

FLORA LICHTMAN: Rachel, are you comfortable talking about your own story?

RACHEL MOSELEY: Yeah, absolutely.

FLORA LICHTMAN: What was your diagnosis experience? When were you diagnosed, and how?

RACHEL MOSELEY: Yeah, so I was diagnosed when I was 28. And it’s a bit of a funny and embarrassing story, really. So I was taken to many, many clinicians when I was a child. I didn’t make eye contact. I appeared to be deaf, which is a very common thing when autistic children don’t respond to their name, for instance, and they don’t respond to other people.

So there were signs from when I was less than a year old. My mum knew that something was different. And I was taken to many, many specialists throughout my childhood. And autism was the working diagnosis at one point. And so they didn’t put me forward for an assessment. And I didn’t know what the working diagnosis had been.

So I go off, grow up, do psychology at university, and I’m fascinated by autism. And I have a huge degree of empathy for people who struggle to fit in, who have all the struggles of autistic people. So I do my PhD in autism. I learn how to diagnose people as autistic. I still have no idea that I was considered to be autistic. It’s not until– I know. This is what–

FLORA LICHTMAN: So you’re studying it, and you don’t know.

RACHEL MOSELEY: I know. This is what I mean. It’s so embarrassing.

FLORA LICHTMAN: No, it’s not. It’s not. It’s not.

RACHEL MOSELEY: Well, it was only when I started studying autism in girls and women, and my mum just happened to say, well, you know that autism was the working diagnosis for you when you were a child? And it was like a lightbulb moment. I now knew about autism in girls and women. I sought a private diagnosis. I got diagnosed. And when I told people, they were like, yeah. Yeah, I know that. We knew.

FLORA LICHTMAN: [CHUCKLES] What did it mean for you to get that diagnosis? I hear you just gave a big exhale. Was it important for you to have that diagnosis?

RACHEL MOSELEY: Very much. Very much. It was important for me and also for my family. So I, like I mentioned other autistic people in research, I grew up believing that there was fundamentally something deeply bad and rotten about myself. And I didn’t understand what. And I had various hypotheses over the years. So for instance, at one point, I knew I was bad, and I knew that psychopaths in the movies are the bad guys. So I thought I must be a psychopath. No, massively, terribly negative view to have of yourself, and I knew that I must hide this. I must not let everyone else know how bad I am.

And from the parents’ side, you often hear and you’re told again and again that you’re just not trying hard enough. I felt like a kind of cancer in my family. I felt terrible. And so you don’t have an explanation for that. You just carry the blame. So getting a diagnosis is like vindication. It’s like a verdict of not guilty.

FLORA LICHTMAN: Hmm. Thank you for sharing that, Rachel. That’s really profound. I mean, and it makes clear how important research, like the research we’ve been talking about, is for people’s lives.

RACHEL MOSELEY: Mm, very much so. And it comes so late for a lot of autistic women. It comes too late for some. And so it’s so important that the world stops seeing autism as a deficit, and instead sees that autistic people have always been here, and they always will be. It’s a natural type of neurological variety. And autistic people have made wonderful contributions, and they will continue to do so. But society has to stop breaking them.

FLORA LICHTMAN: Dr. Rachel Moseley is a researcher in psychology at Bournemouth University in the UK. Rachel, thank you so much for joining me today. It was an immense pleasure.

RACHEL MOSELEY: Thank you so much for having me.

FLORA LICHTMAN: This episode was produced by Rasha Aridi. Special thanks to Ira Kraemer for consulting on this episode. We’ll catch you next time. I’m Flora Lichtman.

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