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Growth models for subtests of the Stanford-Binet Intelligence Scale, 4th edition ( R. L. Thorndike, E. P. Hagen, & J. M. Sattler, 1986a , 1986b ) were developed for individuals with Down syndrome. Models were based on the assessments of 208 individuals who participated in longitudinal and cross-sectional research between 1987 and 2004. Variation in performance among individuals was large and significant across all subtests except Memory for Sentences. Scores on the Memory for Sentences subtest remained low between ages 4 to 30 years. Greatest variation was found on the Pattern Analysis subtest, where scores continued to rise into adulthood. Turning points for scores on the Vocabulary and Comprehension subtests appeared premature relative to normative patterns of development. The authors discuss development at the subdomain level and analyze both individual and group trajectories.
Couzens et al. (Sun,) studied this question.