The role of age at assessment, developmental level, and test in the stability of intelligence scores in young autistic children.

Longitudinal comparisons were made of intelligence and developmental quotient (IQ/DQ) scores for three age groups of 70-72 autistic children aged 2 to 3, 4 to 5, and 6 to 7 years at initial assessment and reassessed at least 2 years later. Stability and predictability over a mean follow-up period of 5 years were related to age, developmental level, and test used at initial assessment. IQ/DQs during preschool years were quite stable and predictive of later IQ scores, except when early scores on the Bayley Scales of Mental Development were compared with later scores on performance or nonverbal tests. As for other populations, predictability for young autistic children was strongest when the same test was used at both assessments, and when children were 4 years or older at initial assessment.