語彙多様性を表す指標の妥当性に関する研究 : 日本人大学生の書き言葉コーパスの場合(公募プロジェクト研究)

概要

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The aim of this study is to investigate the validity of two indices expressing the degree of lexical variation. One is the type/token ratio (TTR), which has been commonly used in the field of applied linguistics including Second Language Acquisition. Recent studies in SLA, however, have questioned its validity, and another index was developed to compensate for its weakness. The new index is a modified version of the type/token ratio, having the denominator changed to the square root of the number of tokens doubled. This study statistically examined whether these two indices are valid measures of the quality of L1 Japanese compositions. One hundred L1 compositions written by Japanese students were collected and digitized to construct a corpus for quantitative analysis. Each composition was subjectively scored by three independent raters of Japanese language experts, on the one hand, and a computer program computed its type count, token count ,and two measures of lexical variation, on the other. Spearman's rank-order correlation coefficients were computed to see how much these five variables correlate with each other. The results gave statistical support the validity of the new index. There was almost no correlation between the subjective scores and the traditional type/token ratio. This suggests that the new index should be used for the measurement of language products instead of the traditional measure.