Comparative Lexical Diversity Metrics in High Stakes English Proficiency Examinations including IELTS and TOEFL

Abstract

Lexical diversity is quite significant in reflecting language proficiency in high-stakes English tests that depict whether a candidate is capable of knowing and using various and appropriate vocabulary. However, there is very little comparative linguistic research on investigating the differences in lexical diversity of the major proficiency tests. This research fills this gap with a comparison and analysis of lexical diversity measurements of IELTS and TOEFL answers. It involves a corpus-based methodology, where with the help of computational tools, Type-Token Ratio (TTR), Measure of Textual Lexical Diversity (MTLD), Hypergeometric Distribution D (HD-D), and VOCD are measured. Results show that IELTS answers are more lexical than TOEFL answers, which are more controlled lexical due to integrated task designs. These results highlight the impacts of the test design on the production of language. Language test evaluation studies also utilize the research paper to offer information on how to improve test scores, scoring rubrics, and how a pedagogical approach to English language learners may be provided in the high-stakes testing environment.