Modifying the social responsiveness scale for adaptive administration

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.