Does the Extreme Male Brain Hypothesis of Autism Apply More to Females Than Males? A Systematic and Meta-Analytic Approach

Abstract

The extreme male brain (EMB) hypothesis posits that autism risk is mediated by high systemizing and low empathizing. This hypothesis has accrued extensive support, but the degree to which it applies in females compared to males, and the relative extent to which autism is associated with empathizing compared to systemizing, is unclear. Systematic review and meta-analyses of studies measuring the empathy quotient (EQ), the systemizing quotient (SQ), and the autism quotient (AQ), among individuals with autism and neurotypical individuals, were used to address these questions. Analyses of results from 34 studies indicated that: (1) Females show larger proportional differences in EQ and SQ between ASD and NT individuals than do males, (2) EQ shows larger proportional differences between autism spectrum (ASD) and neurotypical (NT) individuals than does SQ, (3) sex differences in EQ and SQ are highly attenuated among individuals with ASD, especially for SQ in females, (4) the regressions of EQ and SQ on AQ show significantly steeper slopes among individuals with ASD than in NT individuals, and (5) across studies, EQ and SQ are inversely associated among individuals with ASD, but not in NT individuals. These results provide new insights into the causes of ASD and its male bias.