Predicting Expressive Vocabulary Acquisition in Children With Intellectual Disabilities: A 2-Year Longitudinal Study

Purpose: This study's objectives were to describe expressive vocabulary acquisition in children with intellectual disabilities (ID) and to examine specific pre-and early linguistic behaviors used to request and comment, chronological age, cognitive skills, and vocabulary comprehension as predictors of expressive vocabulary. Method: This study included 36 children with ID, age 3;00 (years;months) to 6;05, with an average initial expressive vocabulary of 67 words. Expressive vocabulary acquisition was longitudinally followed over a 2-year period based on 4-monthly administrations of the Dutch version of the MacArthur Communicative Development Inventory/Words and Gestures (I. Zink & M. Lejaegere, 2002). Specific pre-and early linguistic behaviors used to request and comment as well as cognitive skills and vocabulary comprehension were measured at baseline. Results: Individual growth modeling indicated that vocabulary comprehension was the only unique predictor of initial expressive vocabulary. Subsequent vocabulary growth was uniquely predicted by proportion of bimodal gesture + vocalization comments, chronological age, and cognitive skills. Conclusions: The results of this study underscore the great heterogeneity in expressive vocabulary skills in children with ID. The importance of prelinguistic communication, chronological age, cognitive skills, and vocabulary comprehension for explaining differences in expressive vocabulary skills is discussed.