Psychometric Evaluation of Lexical Diversity Indices: Assessing Length Effects Purpose Several novel techniques have been developed recently to assess the breadth of a speaker's vocabulary exhibited in a language sample. The specific aim of this study was to increase our understanding of the validity of the scores generated by different lexical diversity (LD) estimation techniques. Four techniques were explored: ... Research Article
Research Article  |   June 01, 2015
Psychometric Evaluation of Lexical Diversity Indices: Assessing Length Effects
 
Author Affiliations & Notes
  • Gerasimos Fergadiotis
    Portland State University, OR
  • Heather Harris Wright
    East Carolina University, Greenville, NC
  • Samuel B. Green
    Arizona State University, Tempe
  • Disclosure: The authors have declared that no competing interests existed at the time of publication.
    Disclosure: The authors have declared that no competing interests existed at the time of publication.×
  • Correspondence to Gerasimos Fergadiotis: gfergadiotis@pdx.edu
  • Editor: Rhea Paul
    Editor: Rhea Paul×
  • Associate Editor: Thomas Klee
    Associate Editor: Thomas Klee×
Article Information
Language Disorders / Language / Research Articles
Research Article   |   June 01, 2015
Psychometric Evaluation of Lexical Diversity Indices: Assessing Length Effects
Journal of Speech, Language, and Hearing Research, June 2015, Vol. 58, 840-852. doi:10.1044/2015_JSLHR-L-14-0280
History: Received October 4, 2014 , Revised January 24, 2015 , Accepted February 4, 2015
 
Journal of Speech, Language, and Hearing Research, June 2015, Vol. 58, 840-852. doi:10.1044/2015_JSLHR-L-14-0280
History: Received October 4, 2014; Revised January 24, 2015; Accepted February 4, 2015

Purpose Several novel techniques have been developed recently to assess the breadth of a speaker's vocabulary exhibited in a language sample. The specific aim of this study was to increase our understanding of the validity of the scores generated by different lexical diversity (LD) estimation techniques. Four techniques were explored: D, Maas, measure of textual lexical diversity, and moving-average type–token ratio.

Method Four LD indices were estimated for language samples on 4 discourse tasks (procedures, eventcasts, story retell, and recounts) from 442 adults who are neurologically intact. The resulting data were analyzed using structural equation modeling.

Results The scores for measure of textual lexical diversity and moving-average type–token ratio were stronger indicators of the LD of the language samples. The results for the other 2 techniques were consistent with the presence of method factors representing construct-irrelevant sources.

Conclusion These findings offer a deeper understanding of the relative validity of the 4 estimation techniques and should assist clinicians and researchers in the selection of LD measures of language samples that minimize construct-irrelevant sources.

Acknowledgments
This research was partially supported by National Institute on Aging Grant R01AG029476. We are especially grateful to the study participants. We also thank the volunteers in the Aging and Adult Language Lab at Portland State University for assistance with language analyses.
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