Lexical and Syntactic Complexity across Adjacent IELTS Writing Task 2 Band Levels:  A Corpus-Based Study

Abstract

Lexical and syntactic complexity are important indicators of second language writing proficiency, particularly in assessment-oriented contexts such as IELTS Writing Task 2. However, limited attention has examined whether selected complexity measures can distinguish closely related IELTS band levels. A small-scale learner corpus of 30 essays, with 10 essays per band level, was analyzed quantitatively. Lexical diversity was measured using the Measure of Textual Lexical Diversity (MTLD), lexical sophistication was operationalized as the percentage of Academic Word List (AWL) items, and syntactic complexity was assessed through mean sentence length (MSL). One-way ANOVA showed a significant difference in lexical diversity, whereas AWL percentage and MSL showed non-significant upward trends. Post-hoc comparisons indicated that the significant MTLD difference occurred between Bands 6 and 8 rather than between immediately adjacent bands. Because the corpus consists of band-labeled instructional essays, the findings should be interpreted as exploratory rather than generalizable evidence of IELTS band distinctions.