Are there really more boys than girls with autism?

Ever since scientists in the 1940s first started to discuss autism the difference in the ratio of boys to girls who receive the diagnosis has been recognised. Early studies indicated that the ratio was as high as 10:1. The initial explanation for this was a simple one, that because males only have one X chromosome they are more at risk; should a fault occur on the X chromosome in a stretch of DNA they would develop autism, but should a girl develop the same fault then they have another X chromosome to compensate for it. The hunt for the ‘X factor’ never bore fruit however.

Current thinking now proposes that the ratio is much lower, with figures ranging between 3.35 and 4 to 1, with the highest differences being between boys and girls with higher IQs. Modern suggestions for the difference suggest that it may be due to a combination of biological, diagnostic and phenotype differences.

The Protective Female Effect 

The idea of the ‘protective female effect’ is in part an evolution of the theory that boys simply have a greater chance of developing autism than girls, however it relies less heavily on a misinformed genetic explanation. Scientists are now focused more on the idea that there is a protective characteristic of females in general. This is due to the fact that from as young as nursery age females are more aware of social behaviour. They watch and mimic those around them to a greater degree than males, which means that those with a lesser degree of intellectual disability are more able to mask their autism, even if doing so is subconscious.

Masking and Missed Diagnosis 

Masking is another reason that the sex ratio of autism diagnosis tends to be skewed in favour of males. Masking, as mentioned above, is the ability for some to hide or mask their autism as they mimic social interactions that they see around them, even if they do not understand them or would otherwise not do them. This makes it much harder to identify those girls with autism who have higher IQs, as it can often seem as though they do not to display the typical social difficulties of someone with the condition.

This is evidenced by the fact that when we look at focus groups of those with autism who have a lower IQ, and thus present with more severe symptoms, the gap between the diagnosis rate of boys to girls is much lower. The increased ability for girls of a higher IQ to compensate for some of their difficulties leads many to suspect that we are simply not identifying them, or that they are being increasingly misdiagnosed with conditions such as anxiety instead.

Diagnostic Criteria 

Some researchers also theorise that the diagnostic criteria that is most commonly used when assessing children for autism spectrum disorders is fundamentally biased towards males, as most clinical studies have been done with male participants and thus the stereotype formed is a male one. This bias can be seen in some of the questions that are often asked in a diagnostic interview, such as in the behaviours section. One of the questions asked is “Is s/he unusually interested in things like metal objects, lights, street signs or toilets?” The answer is probably not, though the examples given mean that any obsessive interests that may be seen as more ‘typically female’ may be missed. The child may have an unusual interest in hair brushes or glitter, but this is seen as ‘normal’ for girls to be interested in or simply disregarded by the parent as not symptomatic. Another such example is “Will s/he play with the whole toy or does s/he seem interested in one part of the toy, such as spinning car wheels or opening and shutting the doors?” Again the questions is slightly leading, as parents may answer no even though the only thing that their child does with her dolls is change their shoes repeatedly rather than playing with the whole toy.

So what really is the ratio? 

It is impossible to be 100% sure what the ‘real’ ratio of females to males who have autism is and research into the question continues. It is generally accepted that yes, there may be more boys with autism, but that the ratio is no where near as high as previously believed. The most comprehensive investigation of the matter was a study that compiled the work of 54 studies carried out world wide to do a comprehensive analysis of the findings of all of them. In total it included almost 14 million participants, including 53,712 children with autism. The prevalence was suggested to be around 4.2 boys to every 1 girl with autism. However more than half of the studies that were conducted did not evaluate the children for autism themselves, and the diagnosis was gained by passive means, such as parent statements, old medical records or school evaluations. In the cases in which researchers evaluated the participants themselves, it fell to a lower ratio of around 3.25 boys to every 1 girl.