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Our goal was to study early identification of language disorders by measuring longitudinal trajectories of vocabulary size and syntactic ability (i.e. content and function words). We performed latent class analyses (LCAs) on two MB-CDI datasets, one of which contained diagnostic status (Dx) for a subset of participants. Estimating only on total inventory, the overlap in trends between Dx+ and Dx- was too large to assign a “potential diagnosis” group. However, performing separate LCAs on content vs. function word inventory was more informative. While the majority of participants were assigned to equal-rate classes, a small number were assigned to classes with large or small functional inventories for concrete inventory size. A significant group of Dx+ participants appeared in a class which included 43 participants from the other dataset, only 7 to 11 of whom would have been otherwise identified with the Delay 3+ criteria. Participants in this group had significantly lower Mullen receptive (d=.66) and expressive (d=.49) language scores. These findings provide some avenues for early identification of language delays in longitudinal samples. |
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