Identifying Key Linguistic Variables of Second Language Speaking Proficiency Using Principal Component Analysis

This study conducted principal component analysis (PCA) to identify key linguistic factors distinguishing the speaking proficiency levels of Korean learners grouped by CEFR classifications. The PCA primarily focused on fluency, lexis, and complexity, with particular emphasis on syntactic complexity. The analysis revealed that PC1 explained the largest variance (31.6%) in proficiency levels, with syntactic complexity—measured as complex nominals per T-unit (CNT)—emerging as the most significant differentiating factor. An analysis of variance (ANOVA) confirmed statistically significant differences in CNT across proficiency levels, underscoring its critical role in evaluating grammatical ability. Fluency variables, such as articulation rate, and lexis variables, including lexical diversity, although statistically non-significant, provided valuable insights into learners’ broader proficiency development. The results also indicated that higher proficiency levels were associated with greater use of syntactically complex structures, highlighting the importance of grammatical sophistication in second-language speech. Additionally, learners at lower proficiency levels relied more on simple sentence constructions, which suggests a gradual progression in syntactic complexity as proficiency increases. These findings emphasize the pivotal role of syntactic complexity in assessing speaking proficiency and suggest that incorporating such measures into language evaluation frameworks could provide a more comprehensive and nuanced reflection of learners’ linguistic development. This, in turn, could facilitate the design of targeted instructional strategies and assessments that align more closely with learners’ developmental trajectories, addressing specific gaps in their linguistic skills.