The autism sex ratio

Historically and even today, males have been diagnosed with autism more frequently than females. The first studies in autism even featured almost exclusively boys.^[1]Die schizoiden Psychopathien im Kindesalter (Sukhareva, 1929)^[2]Autistic Disturbances of Affective Contact (Kanner, 1943)^[3]Die “Autistischen Psychopathen” im Kindesalter (Asperger, 1944) But is autism really more prevalent among men, or is there a diagnostic gender bias? Moreover, can it fully account for the ratio we see between males and females?

In this article, I will explore the latest research on the sex ratio in autism and look at the different factors contributing to male bias. Why does autism still seem more prevalent in men?

NB: For the sake of simplicity, men and women (and male and female) will be discussed as biological categories in this post. This is not an endorsement of binary conceptions of sex or gender. However, the complexity of a comprehensive conception of sex and gender is beyond this article’s scope.

Sex ratio

The male-to-female ratio for autism has long been estimated to be 4:1.^[4]Epidemiology of Pervasive Developmental Disorders (Fombonne, 2009) However, the diagnostic criteria were developed primarily based on autistic males. As our understanding of autism increases and autism in women is studied more, the hope is—and the goal should be—that the diagnostic criteria will be refined so autistic women will be identified more readily. Dr. Natalie Engelbrecht has contributed to the refinement of diagnostic criteria for females in Canada, but there needs to be significantly more public awareness; perhaps especially, there needs to be a better understanding by medical professionals of how autism presents in females. Some researchers suggest that when autism in females is diagnosed effectively, the sex ratio will change to 2:1.

Based on research from 2016, the CDC reports that 1 in 54 children in the US is autistic.^[5]Data & Statistics on Autism Spectrum Disorder | CDC With the current male-to-female ratio, we would thus expect that for every 38 boys, one of them will be autistic; and 1 out of every 152 girls. However, with the suggested sex ratio of 2:1, we might expect 1 out of every 76 girls to be autistic.

In a systematic review and meta-analysis from 2017, Rachel Loomes, Laura Hull, and William Mandy analyzed 54 prevalence studies (comprising 13,784,284 participants, of whom 53,712 were autistic) and found that:^[6]What Is the Male-to-Female Ratio in Autism Spectrum Disorder? A Systematic Review and Meta-Analysis (Loomes, Hull, Mandy, 2017)

• The overall male-to-female ratio was 4.2 to 1.
• High-quality studies had a lower male-to-female ratio of 3.32 to 1.
• Studies that screened the general population irrespective of an autism diagnosis showed a lower male-to-female ratio, of 3.25 to 1.
• Studies that only screened participants with a pre-existing autism diagnosis showed a higher male-to-female ratio of 4.56 to 1.

The researchers conclude that the actual male-to-female ratio is not 4:1—as is often assumed—but is likely closer to 3:1. More recent research, however, shows that the ratio looks more like 2.5:1.^[7]Male to female ratios in autism spectrum disorders by age, intellectual disability and attention-deficit/hyperactivity disorder (Posserud et al., 2021) But these ratios aren’t static; a Norwegian study from 2021 looked at 2.5 million children and adults (born before 2011) and found that as autistics age, the male:female sex ratio decreases.^[8]Male to female ratios in autism spectrum disorders by age, intellectual disability and attention-deficit/hyperactivity disorder

Male bias

So what accounts for the different occurrence rates of autism in men and women? The table below shows various factors that explain why autism is diagnosed less in females than in males—based on genes, epigenetics, and environment. Nevertheless, that does not account for the underdiagnosis and misdiagnosis we see in autistic women.

Not only are fewer girls diagnosed with autism, but they are diagnosed later than males on average. ^[9]Sex Differences in the Timing of Identification Among Children and Adults with Autism Spectrum Disorders (Begeer et al., 2012)^[10]Gender ratio in a clinical population sample, age of diagnosis and duration of assessment in children and adults with autism spectrum disorder (Rutherford et al., 2016) Many escape diagnosis until later in life. Below I describe the main reasons why autism is often overlooked in women.

Autism Awareness

It often takes a while to figure out that we are autistic, especially for those who were born at a time when autism awareness was very low.

When I mentioned the possibility to my psychiatric nurse, she actually laughed at me… I asked my mum, a GP at the time…if she thought I was autistic. She said, “Of course not”. At the time, a good ten years ago now, there just was not much information about how girls presented, and from what she knew, I was nothing of the sort.^[11]The Experiences of Late-diagnosed Women with Autism Spectrum Conditions: An Investigation of the Female Autism Phenotype (Bargiela, Steward & Mandy, 2017)

Camouflaging

For women in particular, this realization can come late in life because many have camouflaged their autistic proclivities and have managed well in life and their careers. Nevertheless, there tends to be a breaking point or circumstances that urge us to seek a diagnosis. For that reason, it is important that we can get access to qualified health professionals that understand autism. For more information on camouflaging, have a look at this post:

Autism & camouflaging

Special interests

There is also evidence that autistic women tend to have fewer eccentric or peculiar interests than their male counterparts,^[12]The complete guide to Asperger’s syndrome (Attwood, 2007)^[13]The biology of the autistic syndromes (Gillberg & Coleman, 2000)^[14] A Guide to Asperger Syndrome (Gillberg, 2002)^[15] Schizoid Personality in Girls: A Follow-Up Study–What are the Links with Asperger’s Syndrome? (Wollf & McGuire, 1995) or may have fewer stereotyped activities.^[16]Sex differences in autism (Lord, Schopler, & Revicki, 1982)^[17]DSM-III and DSM-III-R diagnoses of autism (Volkmar et al., 1988)

Stereotypes

Another problem autistic women—and autistic people in general—face is being confronted with persistent autism stereotypes. Young women felt that “Rain Man” stereotypes—which incorrectly assume that autism is always associated with savant skills and with interest in mathematics and science—had delayed their diagnoses.^[18]The Experiences of Late-diagnosed Women with Autism Spectrum Conditions: An Investigation of the Female Autism Phenotype (Bargiela, Steward & Mandy, 2017)

I’ll never forget my special needs teacher saying
I am too poor at maths to be autistic.

Health professionals

All too often, when (autistic) women approach their health professionals, their concerns are dismissed. A study of 14 late-diagnosed autistic women revealed that five of them reported that after researching autism and deciding to pursue a diagnosis, their family doctor (or GP in the UK) dismissed their concerns and did not offer further support.

Co-occurring conditions

Diagnosis with a co-occurring condition can also lead to underdiagnosis of autism in females.^[19]A Behavioral Comparison of Male and Female Adults with High Functioning Autism Spectrum Conditions (Lai et al., 2011)

Misdiagnosis

Autistic women are often misdiagnosed as well:^[20]The Experiences of Late-diagnosed Women with Autism Spectrum Conditions: An Investigation of the Female Autism Phenotype (Bargiela, Steward & Mandy, 2017)

You go to your doctor… and you get diagnosed with multiple personality disorder which is completely opposite to what you are.

Camouflaging

Women and men with autism often have difficulty socializing. As a way to cope with social situations, many women describe putting on a mask or adopting a certain “persona”^[21]The Experiences of Late-diagnosed Women with Autism Spectrum Conditions: An Investigation of the Female Autism Phenotype (Bargiela, Steward & Mandy, 2017)

I honed something of a persona that was kind of bubbly, vivacious, and maybe a bit dim, because I had nothing to say other than adult novels. So I cultivated an image, I suppose, that I brought out to social situations as my partner’s girlfriend, that was not ‘me’.

Camouflaging/masking is also used to hide autistic traits to appear “normal”, which is to say behaving in accordance with neurotypical norms and expectations. One woman explained using a mask as a double-bluff method to openly joke about behavior her peers might have labeled autistic: ^[22]The Experiences of Late-diagnosed Women with Autism Spectrum Conditions: An Investigation of the Female Autism Phenotype (Bargiela, Steward & Mandy, 2017)

I’ll mask if I act weird—which is typical
of autism; I’ll make a joke about it.

As autistics develop coping mechanisms to maintain their masks. According to one autistic woman, drinking freed her up to maintain her neurotypical mask in situations such as watching television shows she disliked in order to maintain the conversation. Television characters, magazines, books on body language, and novels were all described as media sources that helped women learn how to mask. Another autistic woman described learning phrases and facial expressions from fictional literature to manage social situations.

For more information on using television and literature to learn social scripts, have a look at the following post:

Autism & movie talk