Social factors can play a key role in whether or not a child is diagnosed as autistic, a new study has found.

Boys were more likely to receive a diagnosis of autistic spectrum disorder (ASD) than girls, even when symptoms were equally severe, according to researchers at the universities of Exeter and Bristol.

"We wanted to find out what distinguishes those children without diagnosis but with autistic traits from those who have received a formal ASD diagnosis in the clinic," explained lead researcher Ginny Russell, from Egenis at the University of Exeter. "We thought that there may be social and demographic factors that explain why some children are diagnosed and others are not. Understanding social factors that act as access barriers may provide useful insights for clinicians in practice."

The researchers examined data from a long-term study, the Avon Longitudinal Study of Parents and Children and have published their findings in the journal Social Psychiatry and Psychiatric Epidemiology.

Ginny Russell explained: "Boys were more likely to suffer from severe autistic traits, whether diagnosed with an ASD or not. However, even with the severity of autistic traits held constant, boys were still significantly more likely to receive an ASD diagnosis than girls.

"Boys are more than four times more likely to have ASD and are clearly more likely to suffer from these types of symptoms. More interesting is our finding that even with symptom severity held constant, there is still a gender bias towards diagnosing boys. Our analysis suggests that girls are less likely to be identified with ASD even when their symptoms are equally severe." The researchers suggested that the popular conception of autism as a 'male' disorder may contribute to this bias.

The study also found that the average age of mothers of children with an ASD diagnosis was three years higher than in the population generally.

The association between maternal age and ASD diagnosis was stronger than that between maternal age and ASD traits per se in the sample. The authors suggested one possible interpretation is that older mothers are better at identifying their children's difficulties and have more confidence in bringing concerns to the clinic. Younger mothers may find it harder to identify problems.

Ethnic origin, maternal class and mother's marital status did not significantly predict a child either having an ASD diagnosis or displaying severe autistic traits.