Properties of Lexical Diversity in the Narratives of Children With Typical Language Development and Developmental Language Disorder

Abstract

Purpose We examined four measures of lexical diversity in the narratives of children with typical language development (TLD) and developmental language disorder (DLD) that comprised the normative sample of the Edmonton Narrative Norms Instrument (Schneider et al., 2005). The purpose was to document the properties of each measure with respect to variations in utterance and sample length, developmental trends, and group differences. Method The sample consisted of 377 picture-elicited, story generation transcripts from children with TLD ( n = 300) and DLD ( n = 77) aged 4–9 years. We extracted the moving-average type–token ratio (MATTR) and the number of different words from the full sample, from samples equated for the number of utterances, and from samples equated for the total number of words. Results MATTR was the only measure to show no relationships to utterance or sample length. All measures showed significant positive growth with age and significant groupwise differences between children with TLD and DLD. However, the magnitude of age effects and differentiation between groups varied considerably across measures. Across measures, there were significant differences in the number of children with DLD who were identified with low lexical diversity relative to their same-age peers in the TLD group. Conclusion The results of this study support the view that different measures of lexical diversity may be appropriate for different clinical purposes. It is important for clinicians to understand how measures of lexical diversity function in order to make educated choices among measures and ensure appropriate interpretation.