Measuring autism in males and females with a differential item functioning approach: Results from a nation-wide population-based study.

Existing screening instruments for Autism Spectrum Disorder (ASD) might be prone to detect a male manifestation of ASD. Here, we examined the 17 items from the ASD domain in the Autism-Tics, ADHD and other Comorbidities inventory (A-TAC) for Differential Item Functioning (DIF). Data were obtained from the Child and Adolescent Twin Study in Sweden (CATSS) in which parents have responded to the A-TAC. Information regarding a registered diagnosis of ASD were retrieved from the National Patient Register. The cohort was divided into a developmental sample for evaluation of DIF, and a validation sample for examination of the diagnostic accuracy of the total ASD domain, and a novel male and female short form. Our main finding included the identification of DIF for six items, three favouring males and three favouring females. The full, 17 item, ASD domain and the male and female short form showed excellent ability to capture ASD diagnoses in both males and females up to the age of nine years. The full ASD domain in A-TAC is psychometrically largely equivalent across sex and the limited differences between males and females diminish the need for a sex-specific scoring when utilizing the 17 item total score.