Applying a Rasch model to the Broad Autism Phenotype Questionnaire: item severity analysis and differential test functioning of the English and Spanish versions

The broad autism phenotype (BAP) represents the elevated but nonclinical levels of autism-related expressions expanding them beyond the disorder threshold towards the general population and it is assessed worldwide using the Broad Autism Phenotype Questionnaire. In this study, we applied a Rasch item response approach to the Spanish and the English BAPQ versions. This approach allows us to test the proper functioning of each version, estimate which BAP behaviours are more likeable at different levels of severity, and study whether BAPQ item's severities and orders could be considered equivalent between both versions. A Spanish community sample of 970 participants and an English of 533 ones completed either the Spanish or the English version of the BAPQ. The results revealed a lack of unidimensionality of the Pragmatic Language subscale in both tests and the Rigid subscale in the English version. Both Aloof subscale versions and the Spanish Rigid demonstrated adequate properties but with several items showing differential functioning in the case of Aloof. We conclude by highlighting the necessity of BAP measurements paralleling the current autism spectrum disorder structure, following the severity-dimensional conceptualization (behaviours are continuously distributed according to their severity), and suitable for being adapted to different languages.