Sex Differences in Repetitive and Restricted Behavior Using the Repetitive Behavior Scale-Revised

Background: Repetitive and restricted behaviors (RRBs) are a core symptom of autism spectrum disorder (ASD). Some studies have found that RRBs occur at lower rates in females, particularly in those with higher IQ. Additionally, females are reported to have more socially accepted interests than males, while males with ASD often present with more atypical motor behaviors, restricted interests, and repetitive use of objects. The association between RRBs and developmental level is well established, and when controlling for age and IQ, these differences are found less consistently. The presence of potential sex differences in presentation and frequency of RRBs may have important implications for early detection and diagnosis of ASD. It is possible that if females present with fewer or different RRBs this could lead to delayed diagnosis or misdiagnosis, negatively affecting their access to appropriate intervention and treatment.

Objectives: To examine potential sex differences in the type and frequency of RRBs after accounting for the effects of age and IQ.

Methods: Participants included 391 children and adolescents with ASD ages 2-14 (319 males, 72 females) participating in a larger research study. As part of the measurement battery, parents completed the Repetitive Behavior Scale-Revised (RBS-R), and IQ was assessed using the Mullen Scales of Early Learning or the Differential Ability Scales-2^nd Edition. A one-way analysis of Covariance (ANCOVA) was performed to evaluate differences between males and females on the RBS-R total score, controlling for age and IQ. A one-way multivariate analysis of covariance (MANCOVA) was conducted to examine potential sex differences on the various subscales of the RBS-R, while controlling for age and IQ.

Results: RBS-R total score was significantly correlated with both age (r=-.006, p=.91) and IQ (r=-.124, p=.049). The ANCOVA revealed a significant difference F(1, 388)=3.90, p=.049, with females obtaining higher RBS-R total scores (M=33.69, SD=22.35) than males (M=28.90, SD=18.12) after controlling for age and IQ. A MANCOVA was conducted with sex as the independent variable and RBS-R subscale scores as dependent variables, and age and IQ as covariates. Females had significantly higher scores than males on the self-injurious behavior subscale, F(1,93.19)= 6.30, p =.013, h²=.016, and the sameness behavior subscale, F(1, 229.27)=6.01, p=.015, h²=.015, but not on any other subscale. However, after taking a more conservative approach and performing a Bonferroni correction (a=.0083), no significant differences in scores were found for any subscale.

Conclusions: The results reveal that there may be differences in type and frequency of RRBs displayed by males and females with ASD. Although sex differences were observed in overall RRB score and two subscales after controlling for age and IQ, these differences did not remain statistically significant after correcting for multiple comparisons. The effect of IQ remained significant following the correction, however, further demonstrating how IQ may account for the previously reported differences in RRBs between males and females with ASD.