To predict L2 writing quality using lexical richness indices: An investigation of learners of Chinese as a Foreign Language

The majority of current lexical richness indices are based on Indo-European languages, especially English, with a lack of research that investigates their applicability to diverse language types. This study examines the applicability of 44 lexical richness indices, based on Indo-European languages, to Chinese, with a specific emphasis on investigating their predictive power for the writing quality of Chinese as a Foreign Language (CFL) learners. The present study reveals that five indices (Number of Different Words, Uber Index, Corrected Verb Variation1, Lexical Frequency Profile, and Verb Sophistication1) assessing English as a second language (L2) can also effectively predict the writing quality of CFL learners, and six indices (Verb Variation, Verb Variation1, Function Words Ratio_ auxiliary, Function Words Ratio_ pronoun, Lexical Density1, and Lexical Density2) may be more suitable for measuring Chinese, but not English. Moreover, transformed indices demonstrate a better capacity to measure L2 Chinese compared to traditional indices. In conducting a preliminary exploration of effective indices for measuring the lexical richness of Chinese interlanguage, this study emphasizes their potential impact on L2 teaching and suggests directions for future research.