Sex Differences in Repetitive and Restricted Behavior Using the Repetitive Behavior Scale-Revised
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-2nd 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.
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