Characterizing the Nature of Alexithymia in Autistic Adults: Validation of the Perth Alexithymia Questionnaire

Background: Alexithymia—a trait characterized by difficulties in emotion processing—is of high interest in the autism field. However, the lack of validated alexithymia measures for autistic individuals limits progress. This study aimed to address this gap by examining the psychometric properties of the Perth Alexithymia Questionnaire (PAQ) across autistic and non-autistic samples. Using the PAQ, we investigated how alexithymia manifests in autistic individuals and its links with poor mental health outcomes (anxiety). Methods: Autistic individuals (who reported having a diagnosis from a health professional; n = 244) and non-autistic individuals ( n = 383; age range: 16–62 years) completed the PAQ and a trait anxiety questionnaire online. We conducted confirmatory factor analysis, item response theory (IRT), and moderated nonlinear factor analyses to investigate the psychometric properties of the PAQ and alexithymia differences between autistic and non-autistic individuals. Regression analyses investigated the relationships between alexithymia and anxiety and whether these relationships differ for autistic or non-autistic populations. Results: As operationalized by the PAQ, alexithymia manifested similarly in autistic and non-autistic individuals, comprising a general alexithymia factor and five subfactors: positively and negatively valenced difficulties identifying feelings, positively and negatively valenced difficulties describing feelings, and externally oriented thinking. All factors exhibited good to excellent classical test theory and IRT-derived reliability. The PAQ did not meaningfully bias scores for autistic individuals, who reported greater alexithymia across all its components. Alexithymia predicted greater anxiety, with nuances regarding externally oriented thinking particularly for autistic individuals. Conclusions: For the first time, our study illustrates that all facets of alexithymia can be validly and comprehensively assessed in autistic populations. As measured via the PAQ, alexithymia manifests similarly across autistic and non-autistic individuals, and on average, autistic individuals have greater challenges across all aspects of alexithymia. The PAQ, therefore, represents a critical assessment advancement for the field, providing a foundation for future work on alexithymia and autism.