The current estimates of male to female diagnosis rates for autism spectrum disorder (ASD) is 5.5 (Dworzynski, Ronald, Bolton, & Happe, 2012). This means that for every five and a half males who are diagnosed with an ASD one female is diagnosed. It has been estimated that rates are closer to 2.5 to 2.2 (Dworzynski et al, 2012; Hill, 2009), which would mean that only half of females with an ASD are being diagnosed.
Russell, Steer, and Golding (2011) found that if both males and females presented with the same symptomology of ASD males were significantly more likely to receive a diagnosis. This effect was found for individuals with classic autism symptoms as well as higher functioning autism symptoms, which clearly shows gender bias in diagnosing females with an ASD regardless of where they are on the spectrum. This bias may even occur before the diagnosis process, with females being referred for diagnosis less than males (Russell et al, 2011).
While the bias may occur across the entire spectrum, one area at higher risk is girls who have an average or above average IQ score (Kopp, Kelly, & Gillberg, 2010). It is interesting that the diagnosis rates of Asperger's syndrome, when looking at both genders together, is approximately a third lower then classical autism (Fombonne, 2004). While it is possible that Asperger's syndrome does occur less frequently in the general population, it is also possible that individuals with Asperger's syndrome, regardless of gender, are being missed in the diagnosis process. Additionally, the decrees in prevalence rates could be significantly impacted by females with higher functioning and average or above IQ scores who qualify for an ASD diagnosis, but do not receive an appropriate diagnosis (Kopp et al, 2010).
One possible reason for the low diagnosis rates of females on the autism spectrum is a different presentation of ASD symptoms across genders (Hill, 2009). This can be seen specifically in the presentation of special interests. Males with Asperger's syndrome tend to hyper focus on a specific topic, which may be seen as extremely unusual such as train schedules or vacuum cleaners. Females with Asperger's syndrome tend to escape into fiction or into imaginary worlds inside their head (Hill, 2009).
Autism spectrum disorder is still thought to be more common in males than in females (Dworzynski et al, 2012). However, the large disparity between genders is being though to be less of a biological basis and more of a barrio for females in receiving a diagnosis (Kopp et al. 2010). It is concerning that that it takes females an average of five years, after first seeking help, to be appropriately diagnosed with ASD (Kopp et al, 2010). That would mean that parents who have become concerned enough to seek help for their ten year old daughter, while in fourth grade, would not receive an appropriate ASD diagnosis for her until she was entering high school. More needs to be done to help professionals identify girls who are on the autism spectrum, and to do so in a timely manner.
References
Dworzynski, K., Ronald, A., Bolton, P., & Happe, F. (2012). How different are girls and boys above and below the diagnostic threshold for autism spectrum disorders? Journal of the American Academy of Child & Adolescent Psychiatry, 51(8), 788-797.
Fombonne, E. (2009). Epidemiology of Pervasive Developmental Disorders. Pediatric Research, 65(6), 591-598.
Hill, A. (2009). Doctors are 'failing to spot asperger's in girls'. London, UK: The Guardian, April 11, 2009.
Koop, S., Kelly, K. B., & Gillberg, C. (2010). Girls with social and/or attention deficits: A descriptive study of 100 clinic attenders. Journal of Attention Disorders, 14(2), 167-181.
Russell, G., Steer, C., & Golding, J. (2011). Social and demographic factors that influence the diagnosis of autistic spectrum disorders. Soc Psychiatry Psychiatr Epidemiol, 46, 1283-1293.
