Autism is usually diagnosed in early childhood, but assessments can be made at any time of life. Diagnosis is generally made by a doctor – usually a clinical psychologist, paediatrician or a psychiatrist.

Previously, autism spectrum disorders were classified into various subtypes, such as Asperger's, based on their severity. Under the latest diagnostic guidelines, the single diagnosis of autism spectrum disorder has now replaced these categories – the severity of each affected person’s condition sits somewhere along the spectrum.

Why are autism diagnoses increasing?

The incidence of autism has been increasing since the 1960s. The main reasons for this are greater awareness of autism and more inclusive diagnostic criteria. 

Autism and gender

Males are diagnosed with autism at a much higher rate than females. A number of hypotheses have emerged in an attempt to explain this. One possibility, put forward by British developmental psychologist Simon Baron-Cohen, is that the autistic brain is an “extreme male brain”. According to this proposal, the low rate of autism in females is because they have “further to go” to acquire an extreme male brain (and therefore autism).

Somewhat similar to the extreme male brain hypothesis is the “female protective effect”, in which females need a greater number of genetic mutations to develop autism. In a study of over 750 families with autistic members, researchers found that females diagnosed with autism had a higher number of genetic mutations than males diagnosed with the same disorder. Another way of thinking of this is that if males and females had the same genetic mutations, males would more likely be diagnosed with autism, suggesting females are protected by an as yet unknown mechanism.

A third possibility is that there is a bias in how autism is diagnosed in males versus females. For example, females may have better social skills in general, and be more verbal; those with relatively poor skills or willingness in these areas may be like a ‘normal’ boy, and so not meet the diagnostic criteria for autism. Alternatively, it may be that females just aren’t referred for diagnosis as often, because parents think autism is extremely unlikely to affect their daughters. 

  What is autism?

  What causes autism?

  Autism signs and symptoms

  Autism treatment