Standardized Severity Scores for the Autism Diagnostic Observation Schedule-Toddler Module

Background: Calibrated severity scores have been created for modules 1-3 of the ADOS as a measure of the construct of “autism” as it is measured on this instrument (Gotham, Lord, & Pickles, 2008). Calibrated severity scores had more uniform distributions across age and developmental level and were less influenced by demographic variables than ADOS raw totals. For modules 1-3, severity scores have demonstrated usefulness creating more homogeneous groups for clinical, genetic, and neurobiological research. Calibrated severity scores are needed for the ADOS-T to expand comparisons of ASD behaviors over time.

Objectives: Standardize ADOS-T raw scores to approximate a metric of ASD-related symptom severity that is less influenced by chronological age, language level and nonverbal IQ.

Methods: Data from participants in three independent samples from Michigan, Wisconsin, and Minnesota were combined for these analyses. Analyses were conducted using ADOS-T and psychometric data for 220 children age 12 to 30 months, some with repeated assessments for a total of 488 cases. Following procedures informed by Gotham and colleagues (2008), the ASD sample (N=198) was divided into groups based on chronological age and language level. Within each group, raw scores were mapped onto a severity metric, using percentiles of raw totals corresponding to ADOS-T classifications.

Results: Comparisons across age and language groups suggest Toddler calibrated scores were more uniform and less related to developmental and demographic variables. Preliminary findings indicate calibrated severity scores will be useful for comparison of assessments across raters, modules, and time.

Conclusions: ADOS-T calibrated scores demonstrated reduced associations with age and developmental level. ADOS-T calibrated scores may facilitate longitudinal studies by allowing comparisons to be made starting at 12 months, expanding the ability to identify trajectories of ASD symptoms potentially at the first signs of concern. Calibrated severity scores for the ADOS-T should be replicated in large independent samples. Toddler severity scores should be tested for validity in predicting outcomes (eventual ASD diagnosis, response to intervention).