title: Lexical diversity in the spontaneous speech of children with specific language impairment: application of D.
abstract: The lexical diversity of children with specific language impairment (SLI) (ages 3 years 7 months to 7 years 3 months) was compared to that of normally developing same-age peers and younger normally developing children matched according to mean length of utterance in words (MLUw). Lexical diversity was calculated from spontaneous speech samples using D, a measure that uses repeated calculations of type-token ratio (TTR) to estimate how TTR changes as the speech samples increase in size. When D computations were based on 250-word samples, developmental differences were apparent. For both children with SLI and typically developing children, older subgroups showed higher D scores than younger subgroups, and subgroups with higher MLUws showed higher D scores than subgroups with lower MLUws. Children with SU did not differ from same-age peers. At lower MLUw levels, children with SLI showed higher D scores than younger typically developing children matched for MLUw. The developmental sensitivity of D notwithstanding, comparisons using 100-utterance samples, in which the number of lexical tokens varied as a function of the children's MLUws, and comparisons between 250- and 500-word samples revealed the possible influence of sample size on this measure. However, analysis of the effect sizes using smaller and larger samples revealed that D is not affected by sample size to the degree seen for more traditional measures of lexical diversity.
authors.affiliation: Purdue University, West Lafayette, IN 47907, USA. ajowen@purdue.edu
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Owen
authors.forename: Laurence B
authors.initials: LB
authors.lastname: Leonard
mesh_terms: D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007806:Language Disorders / Q000175:diagnosis*; D008297:Male; D013060:Speech; D013068:Speech Production Measurement; D014825:Vocabulary