Exploring Differences in the Factor Structure of the ADOS-2 By Gender
Autism Spectrum Disorder is diagnosed using the same criteria (e.g., DSM-5, ICD-10) for males and females. An emerging and inconclusive body of literature suggests differences in symptom presentation and related areas (e.g., cognitive ability, behavioral regulation). The consistently disproportionate male-to-female ratio may reflect a true difference in incidence, or suggest that females with ASD are under-diagnosed because of a unique symptom presentation not captured by standardized tools. Conclusions are difficult to make considering limitations in the current body of research, including smaller sample sizes, inconsistencies in participant ages, and the use of mixed sets of measures with a strong reliance on parent report. Currently, most studies within this body of research use the Autism Diagnostic Observation Schedule, Second Edition (ADOS-2), considered the gold standard in direct assessment of autism related symptoms. These studies have reached varied conclusions regarding gender differences as measured by standardized tools, for example, finding no significant gender differences or finding fewer reported repetitive and restricted behaviors (RRBs) (Duvekot et al., 2016). However, to date, there is limited research with large sample sizes of early intervention age children that examines differences in the ADOS-2 algorithm items by gender.
The current study examined the factor structure of the ADOS-2 algorithm items by gender to determine if the Social Affect (SA) and Restricted and Repetitive Behavior (RRB) subscales demonstrate a different factor structure.
A retrospective analysis of evaluation data was conducted from a large, urban sample of early intervention age children who met criteria for ASD. Participants included 252 children, with 177 males and 75 females, (Mage males = 42.4 months; Mage females = 41.2 months). Evaluation measures included the ADOS-2, caregiver interviews, and rating scales. An exploratory factor analysis was conducted to determine if individual items included in the algorithm of the ADOS-2 (Module 1) loaded into the same factors for both males and females. Two factors were forced to align the data with the two subscales of the ADOS-2 (SA and RRB).
Results indicated differences, by gender, in how the algorithm items loaded into the two factors, which likely represent the SA (Factor 1) and RRB (Factor 2) subscales. The greatest differences were noted in Factor 2 (RRB scale), with fewer items loading overall and stronger eigenvalues for specific items (repetitive/stereotyped language) in the female sample. Furthermore, specific items that are included in the RRB subscale on the ADOS-2, did not factor into either structure for females, for example, items that address sensory seeking behavior and repetitive motor movements.
This study illustrates in a large, urban sample of early intervention age children, that female and male presentation as indicated in the ADOS-2 algorithm, load differently on a forced, two factor model. This provides additional evidence to support possible differences in RRB symptom presentation by gender, as measured through the ADOS-2. Future research may include prospective analyses testing the hypothesis that ASD symptom presentation differs as observed on the ADOS-2 algorithm, specifically within the RRB subscale.