We tested the relative levels (i.e., age equivalencies) of concurrent cross-modality (receptive and expressive) vocabulary and the relative strength of the longitudinal, cross-modality associations between early and later vocabulary sizes in minimally verbal preschoolers with ASD. Eighty-seven children participated. Parent-reported vocabulary was assessed at four periods separated by 4 months each. Expressive age equivalent scores were higher than receptive age equivalent scores at all four periods. Cross-lagged panel analysis was used to rule out common, but trivial, explanations for differences between the longitudinal associations of interest. Key associations were tested across intervals that varied from 8 to 12 months. In two of the three tested panels, the associations between early expressive vocabulary size and later receptive vocabulary size were stronger than the associations between early receptive vocabulary size and later expressive vocabulary size, providing evidence that is consistent with the hypothesis that expressive vocabulary size drives receptive vocabulary size in minimally verbal preschoolers with ASD.
© 2015 International Society for Autism Research, Wiley Periodicals, Inc.