Multidimensional Lexical Sophistication in EFL Engineering Students’ Project Proposals: Implications for Genre-Based ESP Instruction

Most studies on the relationship between lexical sophistication and writing quality operationalize lexical sophistication as distributional property of words and focus on argumentative essays. This study examines the various aspects of lexical sophistication of EFL engineering students’ project proposals, comparing them with argumentative essays to explore genre-specific lexical features. Twenty-two indices of various dimensions of lexical sophistication were extracted from both project proposals and argumentative essays written by students with comparable English proficiency. Independent samples t tests revealed significant differences in lexical sophistication between the two genres. An exploratory factor analysis grouped the 22 indices of project proposals into five components. A stepwise multiple regression analysis using these components as predictors suggested that lexical sophistication exhibited limited explanatory power for project proposal quality, contrasting with its established role in general L2 writing contexts. The findings suggest pedagogical implications for ESP instruction, highlighting the integration of discipline-specific terminology, structural coherence, and contextualized function word usage to enhance engineering students’ genre-specific communicative efficacy in project proposal writing.