Purpose
The social responsiveness scale (SRS) is frequently used to quantify the autism-related phenotype and is gaining use in health outcomes research. However, it has a high respondent burden (65 items) for large-scale studies. Further, most evaluations of it have focused on the school-age form, not the preschool form. More validity evidence of shortened forms is necessary in the general population to support the broader health outcomes context of use.
Methods
We evaluated the psychometrics of the SRS in 7030 individuals from multiple predominantly neurotypical samples in order to shorten it based on non-autistic sample metrics. Analyses included item factor analysis, differential item functioning (DIF), and multiple-group item response theory (IRT) to place the SRS items on a comparable scale, which was then simulated via computer adaptive testing (CAT) administration.
Results
The SRS was broadly unidimensional with few methodological residual dependencies. On average, males had more autistic characteristics than females, and preschoolers had fewer characteristics than school-age children. The final IRT calibration included 45 items equated across forms, and each form had 11 with significant wording discrepancies and 9 items with near-identical wording that exhibited form-related DIF. The CAT simulation suggested a median of 14 items was sufficient to reach a reliable score, demonstrating its feasibility across the range of impairments.
Conclusion
IRT allows practitioners the ability to get highly reliable scores with fewer items than the full-length SRS. This supports the future application of the SRS in a computer adaptive testing mode in both neurotypical and ASD samples.
