Psychometric Evaluation of Lexical Diversity Indices in Spanish Narrative Samples From Children With and Without Developmental Language Disorder

Purpose: The purpose of the current study was to examine construct validity evidence for the following 4 lexical diversity measures for use in Spanish narrative samples of children with developmental language disorder and typical language development (TLD): (a) type-token ratio (TTR; Chotlos, 1944; Templin, 1957), (b) hypergeometric distribution D (McCarthy & Jarvis, 2010), (c) measure of textual lexical diversity (MTLD; McCarthy, 2005), and (d) moving-average TTR (MATTR; Covington & McFall, 2010). Method: A multiple-group, confirmatory factor analytic stepwise procedure was applied to examine factorial invariance in a sample of 435 monolingual Spanish-speaking children (335 with TLD and 100 with specific language impairment). Results: MATTR was the strongest indicator of the lexical diversity of a sample and demonstrated measurement invariance across children with TLD and specific language impairment. MTLD scores included some noise at different levels as a function of the length of a sample, especially for short language samples, but differences in relation to MATTR were relatively small. The validity of hypergeometric distribution D and TTR score interpretations was low, as the scores covaried systematically with length, with TTR being the poorest measure of lexical diversity. Conclusion: Results support the use of MATTR and MTLD as measures of lexical diversity and should assist clinicians and researchers in the selection of lexical diversity measures to minimize bias in score interpretations when conducting language sample analyses.