Assessing Autism Symptoms with ADOS Calibrated Severity Scores

Background:  As proposed by Gotham et al. (2008), ADOS calibrated severity scores (CSS) are a standardized metric developed to assess core autism symptoms as a clinical entity distinct from cognitive and adaptive differences.  According to preliminary findings, this metric may provides a means by which to better assess symptoms of autism over time, in both individuals and populations. In the original validation study these scores were shown to be less influenced by factors such as verbal IQ, which accounted for 43% of variance in raw ADOS totals and only 10% in CSS scores.  Despite promising initial work the development of this metric took place within a sample of convenience and as such further study of this metric in additional samples is necessary.

 Objectives:  We aimed to assess the nature of CSS and its relations to current diagnostic categories (i.e., PDD-NOS, autism, Asperger’s Disorder) within a sample of children recruited into an ASD genetics study.

Methods:  Analyses were conducted on data from 227 participants collected through the Simons Simplex Collection site at Vanderbilt University.  Each participating child received a clinical diagnosis of ASD based on a complete psychological evaluation including assessment with the ADOS and ADI-R.  

Results:  In our sample, 111 individuals received a diagnosis of autism, 64 a diagnosis of PDD-NOS, and 52 a diagnosis of Asperger’s Disorder. For the total sample, we found that verbal IQ accounted for 29.16% of variance in raw ADOS totals and only 2.865% of variance in CSS scores, echoing Gotham’s original findings. Similarly, our analyses of raw ADOS totals and CSS scores by age and language map well onto previous results, with the CSS scores showing more uniform distributions. Additionally, we found in our sample a significant difference in CSS scores between those diagnosed with autism and PDD-NOS, while differences between autism and Asperger’s, and Asperger’s and PDD-NOS, were not significant.

Conclusions: Our results indicate that CSS scores appear to be of greater utility than ADOS raw totals in marking the severity of autism symptoms relative to age and language level and independent of cognitive and adaptive differences. CSS scores also map consistently to current autism and PDD-NOS diagnoses. Further directions include analysis of CSS scores from over 60 study participants who did not meet criteria for an ASD.