Meta-Analysis of Sex Differences in Core Symptomatology in Autism Spectrum Disorder

Background: Autism Spectrum Disorder (ASD) has drawn the field’s attention in recent decades, because of its high, quickly increasing, and disproportionate prevalence between the two sexes (e.g., 1 in every 38 males but 152 females; Autism and Developmental Disabilities Monitoring Network). To understand the sexual disparity, researchers have started investigating the various differences in physiological and psychological characteristics between males and females with ASD.

Objectives: The researchers meta-analyzed published studies, focusing on the sexual disparity in the severity of core symptomatology in ASD. Several potential moderators of the disparity, namely, symptom type, patient age, IQ, the assessment tool, diagnostic criteria, and publication year of a study, were also investigated. These moderators can hardly be studied in full in a single empirical study. The present meta-analysis therefore helps not only synthesize but also advance the literature.

Methods: A systematic literature search was performed on PsycINFO, Scopus, PubMed, and Web of Science for empirical studies written in English and comparing males and females with ASD in their symptom severity. The current study then included in total 84,718 (males) and 19,240 (females) repeated measures of symptoms of ASD for males and females respectively; the data were nested in 295 effect sizes nested in 43 independent studies consisting of 9192 males and 2412 females. The moderators of interest were coded if possible for analysis.

Results: Multilevel meta-analysis with effect sizes nested in studies indicated that males demonstrate higher severity in restricted and repetitive behavior but not in other two core symptoms of ASD or the composite severity than do females. This phenomenon was elaborated by the finding that the Autism Diagnostic Observation Schedule (ADOS) assessment specifically detects more restricted and repetitive behavior for males than for females. The same disparity does not emerge for other symptoms or other assessments. Finally, the analyses indicated to a potential age moderation effect that heightens females’ composite ASD severity if they are older than 18. This result, nevertheless, did not appear for any of the three core symptoms individually. No moderation was found for IQ, diagnostic criteria, linear or quadratic publication year.

Conclusions: The results show that males with ASD demonstrate more restricted and repetitive behavior than do females with ASD, and the disparity might be attributed to using ADOS as the assessment tool. Further, different from what the literature suggests, patient age, IQ, the diagnostic criteria, and social-historical context of a study indicated by its publication year do not seem to influence differences in symptom severity between males and females with ASD.