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Are Males and Females with ASD More Similar Than We Thought?
The predominance of autism spectrum disorder (ASD) diagnoses among males, with average estimates suggesting a 4:1 ratio (Baird et al., 2006), is one of the most consistent features of the disorder. Previous research examining gender differences among individuals with ASD has suggested that females with this disorder have lower IQ associated with greater symptom impairment (Fombonne, 2009). However, past gender research has been limited by inconsistent findings, small female sample sizes, reliance on parent report measures, and confounding variables such as age and intelligence (Kirkovski, Enticott, & Fitzgerald, 2013).
Objectives:
The purpose of this study was to examine gender differences in intelligence, age of diagnosis, and symptom severity in a community-based clinic sample. This study attempted to overcome past methodological limitations by using a large sample of females and clinician report measures.
Methods:
Evaluations were conducted across statewide outpatient clinics operated by the University of North Carolina TEACCH Autism Program between January 2001 and March 2013. A total of 679 participants (males=566, females=113) who provided consent for their clinical data to be used for research purposes were selected for analysis. These participants were administered an ADOS, CARS, and an IQ measure and received a DSM-IV clinical diagnosis of Autistic Disorder, Asperger’s Syndrome, or PDD-NOS. Approximately 24% of the sample had an IQ score below 70 (M=85.9), 17% of the sample was female, and the age at time of diagnosis ranged from 5 years, 0 months to 56 years, 4 months.
Results:
When controlling for IQ and age at diagnosis, there was a very small, yet significant, effect of gender on total CARS score, B = .07, t(675) = 2.05, p = .04. Females had an average total CARS score that was 0.92 points higher than for males. When controlling for the effect of IQ and age at diagnosis, there was no effect of gender , B = .06, t(675) = 1.64, p = .10. Overall, there were no gender differences in IQ scores, t(677) = .17, p =.86, or age at time of diagnosis, t(677) = .61, p =.54.
Conclusions:
Overall, these results suggest either very small or no gender differences in IQ, age at diagnosis, or symptom severity. There is a slight difference with females having higher average total scores on the CARS, but this difference is likely of minimal clinical significance based on its extremely small effect size. As this is a large sample representative of a clinical population of individuals diagnosed with ASD, it has substantial power to find potential differences while also taking into account IQ and age of diagnosis factors that have not been consistently controlled for in previous research. These results suggest that gender differences in IQ and ASD symptomatology are likely less important than previously believed.