英語学習者のアウトプットにおける語彙の多様性研究の現在と今後の課題 Current trends and issues of lexical diversity studies in productive texts of English learners
The purpose of this study is to examine the reliability and validity of widely used lexical diversity (LD) measures including type/token ratio (TTR), standardized TTR, Guiraud Index, Herdan Index, D, HD-D, and Measure of Textual Lexical Diversity (MTLD) through a survey of previous studies and discussion. LD refers to the range of vocabulary within a text and avoidance of repetition; it is often considered to reflect the vocabulary proficiency or productive lexical richness of a learner. A serious problem with LD measures is that they are dependent on text length, which indicates a lack of reliability. Even when LD measures overcome the problem of text length, researchers need to carefully examine their validity as developmental measures of the productive vocabulary of second language (L2) learners. This paper also discusses the limitation of LD measures and suggests directions for further studies.
岐阜市立女子短期大学研究紀要 62, 29-38, 2012