Sex/gender differences in autistic restricted and repetitive behaviours and interests

Autistic females are often diagnosed less frequently than autistic males, despite many displaying similar levels of autistic traits to males. Explanations for this include diagnostic assessment tools not being sensitive enough to the manifestation of autistic behaviours in females, as well as higher levels of camouflaging behaviours in autistic females resulting in some autistic traits being missed when using observational or parent/carer/teacher report measures. Consequently, autism research is relatively unrepresentative of autistic females, especially those who report high autistic traits but do not have a clinical diagnosis. Taking a critical realist approach, the aim of this thesis is to explore sex/gender differences in the subdomain of the autism diagnostic criteria; restricted and repetitive behaviours and interests (RRBIs). Research at the broad construct level of RRBIs indicates that autistic females present with fewer RRBIs than autistic males, however the subdomain is large, with a range of narrow constructs within it that are different to each other (e.g., stereotyped behaviours, insistence on sameness, passionate interests, and sensory experiences), warranting deeper exploration at a fine-grained level. Firstly, a systematic review and meta-analysis was conducted to explore sex/gender differences at the narrow construct level of RRBIs in autistic children, adolescents, and adults. This indicated that autistic males presented with significantly more stereotyped behaviours and passionate interests than females. There was also a trend towards autistic females presenting with more sensory experiences. There was no significant sex/gender differences for insistence on sameness. Autistic females also appeared to hold different types of passionate interests to males. It was deemed important to include participants who self-identify as autistic, without a clinical diagnosis (but who report high autistic traits), in the empirical research project, in an attempt to include a group who has previously been excluded from many studies. Likewise, a self-report measure was chosen so that the subjective experiences of autistic individuals could be captured. The empirical research project explored sex/gender differences in two narrow constructs of RRBIs, insistence on sameness (IS) and repetitive sensory motor behaviours (RSMB), in a sample (n = 84) of autistic (diagnosed and self-identifying) and non-autistic 16-25 year olds. Results indicated that autistic females self-report significantly more IS behaviours compared to autistic males and similar levels of RSMB to autistic males. These findings emphasise the importance of exploring RRBIs at a fine-grained level and raises the importance of professionals involved in identification of autism, for example educational practitioners, being aware of sex/gender differences in RRBIs, particularly how these may present in autistic females