Stability of Cognitive and Adaptive Behaviour Standard Scores in Preschool Children with Autistic Spectrum Disorders

Background: In school-aged children with autistic spectrum disorders (ASD), standard scores on cognitive and adaptive measures are considered to provide meaningful prognostic information and may be used to identify intellectual disability. In preschoolers with ASD, the stability of cognitive and adaptive behaviour scores is less clear. New measures may affect the stability of early scores, and increasing access to early intervention may influence developmental trajectories.

Objectives: This study examines the stability of cognitive and adaptive standard scores between the preschool period and age 6 in three cohorts of children initially assessed at age 2, 3, or 4 years.

Methods:  Data came from a longitudinal study of Canadian children with ASD (Pathways in ASD). The present study employs assessment data from age of diagnosis (at 2, 3, or 4 years), approximately one year later, and at age 6. Cognitive skills were assessed using the Merrill-Palmer-Revised Scales of Development (complete data for n = 207), and adaptive skills were assessed using the Vineland Adaptive Behavior Scales, 2nd ed. (complete data for n = 212).

Results: All three cohorts showed large gains in cognitive standard scores by age 6 (p ≤  .001), with mean increases of 19, 17 and 16 points for those initially assessed at ages 2, 3, and 4 respectively. Adaptive behaviour standard scores were more stable, with mean gains of approximately 4 points for 3- and 4-year-olds (p < .001; these changes took place in the year following diagnosis). Fifty-seven percent of 2- and 3-year-olds and 47% of 4-year-olds experienced a significant increase in cognitive functioning (≥ 15 points) by age 6. Significant gains in adaptive functioning were less common, especially for 4-year-olds (~ 14% of 2- and 3-year-olds; 5% of 4-year-olds; p < .001). Significant decreases in scores were observed for some 2-year-olds (14% cognitive; 10% adaptive) and 3-year-olds (13% cognitive; 3% adaptive), and a few 4-year-olds (4% cognitive; 0% adaptive). Additional analyses will explore trajectories of change and predictors of outcome (e.g., intervention variables) using growth curve analysis.

Conclusions: Understanding the stability of measures of ability in children with ASD is important clinically, affecting such decisions as measure selection, feedback to families, and treatment planning. These results suggest caution in using very early standard scores to provide prognostic statements about cognitive ability  – due to potential for significant increases. Adaptive behaviour scores appear more stable, and may provide more useful prognostic information. Changes over time may be influenced by a range of factors, including access to interventions.

Sponsors: Canadian Institutes of Health Research, Autism Speaks, Government of British Columbia, Alberta Innovates- Health Solutions, Sinneave Family Foundation.