Evaluating the Construct Validity of Sentence-Focused Diversity Measures With Late-Talking Toddlers and Same-Age Peers

Purpose: The purpose of this study was to evaluate the construct validity of three sentence-focused diversity measures, intransitive verb diversity, transitive verb diversity, and third person (3P) subject diversity, using two methods: (a) group differentiation of late-talking (LT) toddlers from peers with typically developing (TD) language and (b) associations with established measures of language development. A secondary purpose was to determine whether 3P subject diversity was more strongly associated with intransitive verbs than transitive verbs. Method: Examiner–child language samples from 58 LT toddlers and 82 TD toddlers (ages 24–30 months) were collected using a structured language sampling protocol. Transcripts were coded to obtain measures of intransitive verb diversity, transitive verb diversity, and 3P subject diversity as well as mean length of utterance (MLU) and number of different words (NDW). We used nonparametric tests to examine differences between groups and associations between measures within each group. We also conducted an exploratory analysis using a generalized linear mixed model to determine the strength of associations for intransitive and transitive verb diversity with 3P subject diversity. Results: All sentence-focused diversity measures were significantly different between groups. They were also positively related to MLU, NDW, and to each other within each group. Both intransitive verb diversity and transitive verb diversity were significantly associated with 3P subject diversity, after accounting for NDW; however, the strength of association observed between intransitive verb diversity and 3P subject diversity was nearly twice as large. Conclusions: These findings provide new evidence that sentence-focused diversity measures are valid indicators of early language development and that intransitive verbs have a stronger association with diverse 3P subjects than transitive verbs. The value of adopting measures of verb and subject diversity with LT toddlers is discussed.