Background: Why is autism spectrum disorder (ASD) less prevalent among females than males? We constructed a statistical model for each of both existing classes of theories, and derived competing predictions for the essentialist expression hypothesis (females express less severe ASD traits so are diagnosed less) against the constructivist perception hypothesis (females’ expressions are socially perceived as less severe so are diagnosed less). Specifically, if the expression hypothesis is true, based on our models, diagnosed females should show less severe symptoms than their male counterparts, whereas the reverse should happen if the perception hypothesis is true. Method: We conducted a meta-analysis (Data point N = 117,778 participant N = 16,209) on the differences in ASD symptom severity between females and males diagnosed with ASD, across age groups, IQ ranges, diagnostic criteria, and assessment tools. Results: We found strong new evidence that ASD-diagnosed females and males differ little in symptom severity, even in the face of a found publication bias in favor of reporting males’ symptoms relative to females’ and the common understanding of ASD as a so-called male disorder. Conclusions: We argue the finding supports both classes of theories, implying that they are similar in size, though different in directions, in creating sex differences in symptom severity for diagnosed individuals. The sex disparity in ASD prevalence likely results from both the biological expression of, and the social perception toward individuals’ ASD symptoms.
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