The Autism Diagnostic Observation Schedule Calibrated Severity Score Best Measures Autism Diagnostic Symptom Severity in Pre-School Children

Background: The severity of autism spectrum disorder (ASD) is often measured by co-occurring conditions, such as intellectual disability or language delay, rather than deficits in social interaction, and restricted interests and repetitive behaviors (RRB). The Autism Diagnostic Observation Schedule calibrated severity score (ADOS CSS) was created to facilitate comparison of the diagnostic features of ASD independent of related conditions over time. Previous research found that, compared to the ADOS total score, the ADOS CSS was less influenced by factors such as cognitive and language abilities. Past studies did not include clinical judgment as a measure of ASD severity, nor explore the effect of other variables that may influence ASD severity, such as behavior problems and sleep disturbance.

Objectives: The objective for the current study was to determine whether the ADOS CSS, ADOS total score, or clinical rating of degree of impairment was least influenced by factors other than deficits in social interaction and RRB.

 Methods: Children 2-5 years old were ascertained for the Study to Explore Early Development (SEED) through birth certificate records and multiple sources that serve children with developmental problems. All children were screened for ASD with the Social Communication Questionnaire upon enrollment. Children who demonstrated ASD risk were asked to complete an in-person developmental assessment that consisted of the ADOS and Mullen Scales of Early Learning (MSEL). Caregivers completed the Autism Diagnostic Interview – Revised (ADI-R), Child Behavior Checklist (CBCL), and Vineland Adaptive Behavior Scales. All children classified as ASD met ASD criteria on both the ADI-R and the ADOS, or met ASD criteria on the ADOS and one of three alternate criteria on the ADI-R.

The clinician who administered the ADOS noted his or her judgment of degree of impairment associated with ASD on a 7-point Likert scale (SEED DOI). The effect of child variables (i.e., CBCL externalizing behaviors, internalizing behaviors, and sleep problems; and MSEL expressive language, fine motor, receptive language, and visual reception skills) on measures of ASD severity (i.e., ADOS CSS, ADOS total score, and SEED DOI) were assessed with three separate linear regression models.

Results: 2,600 children completed a developmental evaluation and 707 met the SEED ASD case definition. The total amount of variance in ASD symptom severity accounted for by child characteristics was 9% for the ADOS CSS, 29% for the ADOS total score, and 38% for the SEED DOI. Higher ratings of autism symptom severity were significantly associated with more internalizing behavior problems and fewer expressive language and fine motor abilities for all three ASD severity outcomes. Expressive language ability contributed to ADOS total score and SEED DOI ratings more than any other variable.

Conclusions: Compared to the ADOS total score and clinical judgment, the ADOS CSS was the least influenced by the effects of co-occurring conditions on the severity of ASD diagnostic symptoms. Our findings are in agreement with past studies and suggest that, among the measures we evaluated, the ADOS CSS is the best measure of core features of ASD in pre-school children.