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This study examined the concurrent validity of the Language Development Survey (LDS), a 310-word parent report screening tool for language delay in toddlers, by testing its associations with the MacArthur-Bates Communicative Development Inventories: Words and Sentences (CDI:WS), a 680-word parent report instrument. Participants were 239 toddlers 23-25 months of age. The correlation between total vocabulary score on the 2 instruments was .95, and correlations across comparable semantic categories ranged from .84 to .94. The correlation between the LDS and the CDI:WS for mean length of phrases calculated on 3 examples of the child's longest and best phrases was .90. Both instruments demonstrated that parents reported higher vocabulary and mean phrase length scores for girls. The study indicates that information obtained from the LDS about rank ordering of toddlers in terms of their reported vocabulary and mean length of phrases is equivalent to that obtained from the longer CDI:WS.
Rescorla et al. (Sun,) studied this question.