Background: At IMFAR 2006, we reported our work in standardizing raw ADOS total scores from a large dataset to approximate a severity metric for the construct of ‘Autism’ as it is measured on this instrument. We are now approaching this pursuit with changed methodology.

Objectives: To estimate severity of autism using ADOS scores that have been normalized to reduce the effects of verbal level, chronological age, and IQ.

Methods: Analyses were conducted using ADOS and psychometric data for 1415 children aged 2 to 16 years, some with repeated assessments for a total of 2195 cases. The ASD sample (N=1786 cases) was divided into cells determined by chronological age and language level. Previously, calibrated scores were generated based on percentiles of raw ADOS totals within each cell. In the revised approach, severity scores were based on raw total percentiles corresponding to each diagnostic classification within each age/language cell.

Results: Preliminary findings indicate that new calibrated scores (1) allow comparison of assessments across raters, modules, and time; (2) provide a means of assessing the relationship between severity in ASD and verbal and nonverbal IQ; and (3) may offer another option for identifying homogeneous groups of individuals with ASD for genetic and neurobiological research.

Conclusions: Calibrated severity scores should be replicated in large independent samples, and tested for validity in predicting outcome (treatment responsiveness, school achievement and placement, eventual independence, etc.) in children with ASD.