The relationship between L2 vocabulary knowledge and reading proficiency: The moderating effects of vocabulary fluency

The study's central focus is the intricate relationship between vocabulary knowledge and reading proficiency in the context of second language (L2) acquisition, specifically for English as a Foreign Language (EFL) learners. While the positive impact of lexical knowledge on reading is well-established, the multifaceted nature of vocabulary knowledge presents a challenge. Existing research often distinguishes between vocabulary breadth (quantity of words known) and depth (quality of knowledge about those words). However, studies often overlook the concurrent role of both receptive and productive vocabulary knowledge, and the critical role of vocabulary fluency—the speed and automaticity of word processing—in this relationship remains largely unexplored, especially for Chinese EFL learners who face unique challenges due to linguistic differences. The authors highlight the need for effective methods to help Chinese EFL learners develop their vocabulary knowledge and improve reading proficiency, emphasizing a more purposeful approach to vocabulary learning.

The literature review examines two primary approaches to understanding vocabulary knowledge: the developmental approach (viewing vocabulary acquisition as a cumulative process, often assessed using scales like the Vocabulary Knowledge Scale (VKS)) and the dimensional approach (dividing vocabulary knowledge into components such as breadth, depth, and fluency). The VKS, while widely used, faces criticism due to its assumptions about equal difficulty between levels and linear development. The dimensional approach, exemplified by Nation's framework (2013), categorizes vocabulary knowledge into form, meaning, and use, each with receptive and productive aspects. However, the comprehensiveness of Nation's framework can hinder practical application in research and teaching. Therefore, the authors focus on four dimensions: receptive and productive vocabulary breadth and depth, acknowledging the importance of vocabulary fluency as a distinct yet related dimension. The review highlights the limited research on the role of productive vocabulary knowledge and vocabulary fluency in predicting reading proficiency. Existing studies often rely on meaning-recognition tests, which may overestimate vocabulary size, leading to inconsistent findings regarding the relative importance of receptive versus productive knowledge in L2 reading. The review lays the groundwork for this study, identifying the need for an investigation using more reliable measurement instruments and a consideration of the moderating role of vocabulary fluency.

This quantitative study employed a purposive and simple random sampling method to recruit 312 Chinese university students from six majors (Chinese, preschool education, business, computer, biology, and chemistry) aged 20.5 years old on average. The instruments used included: 1) A modified Vocabulary Levels Test (VLT) for receptive vocabulary breadth (meaning-recall format); 2) A modified Word Association Test (WAT) for receptive vocabulary depth (measuring word parts, multiple meanings, and collocations); 3) A modified controlled-production vocabulary levels test (PLT) for productive vocabulary breadth (recall format); 4) A Definition Completion Test for productive vocabulary depth; 5) A dictation test (VFT) for vocabulary fluency; and 6) The IELTS academic reading test for measuring reading proficiency. The data were collected using pen-and-paper tests. Confirmatory factor analysis (CFA) was performed using AMOS 24.0 to assess the reliability and validity of the measurement models. Pearson correlation analysis explored the relationships between the variables. Structural equation modeling (SEM) was used to determine the effects of the four dimensions of vocabulary knowledge on reading proficiency, both with and without vocabulary fluency as an independent variable. Ping's Single Indicator Interaction method assessed the moderating effect of vocabulary fluency on the relationships between each vocabulary knowledge dimension and reading proficiency.

The CFA results showed good reliability and validity for all measurement models. Pearson correlation analysis revealed the strongest correlation between receptive vocabulary depth (VDT) and reading proficiency (r = 0.513, p < 0.001), followed by receptive vocabulary breadth (VLT, r = 0.480, p < 0.001). Productive vocabulary breadth and depth showed weaker correlations (r = 0.356 and r = 0.364, respectively, p < 0.001). The SEM analysis (without vocabulary fluency as an independent variable) indicated that receptive vocabulary depth had the highest standardized regression coefficient (β = 0.38) in predicting reading proficiency, followed by receptive breadth (β = 0.33). Productive vocabulary dimensions showed smaller effects (β = 0.20 and β = 0.19). The overall model explained 49% of the variance in reading proficiency scores. When vocabulary fluency was included in the SEM as an independent variable, it showed a negligible negative effect (β = -0.02) on reading proficiency. However, using Ping's Single Indicator Interaction method, the study revealed that vocabulary fluency significantly moderated the relationship between all four vocabulary knowledge dimensions and reading proficiency.

The findings support the importance of receptive vocabulary knowledge, particularly depth, in L2 reading comprehension, aligning with some but contradicting other previous research due to differences in measurement instruments (meaning-recall vs. meaning-recognition). The study's finding that whole-word knowledge explains 49% of the variance in reading scores underscores the crucial role of vocabulary in reading proficiency, suggesting a need for balanced vocabulary learning that emphasizes both breadth and depth. The insignificant effect of vocabulary fluency as an independent variable, yet its significant moderating role, suggests that fluency acts as an enhancer rather than a primary determinant of reading success. This supports the idea that acquiring sufficient breadth and depth of vocabulary knowledge is paramount, and fluency then facilitates efficient processing and use of that knowledge.

This study offers valuable insights into the relationship between L2 vocabulary knowledge and reading proficiency. It highlights the significant role of receptive vocabulary depth, the importance of overall vocabulary knowledge in predicting reading success, and the moderating influence of vocabulary fluency on the vocabulary-reading proficiency relationship. The findings have implications for vocabulary instruction and assessment, suggesting a focus on receptive vocabulary knowledge and the development of fluency. Future research could investigate a wider range of vocabulary depth aspects, use multiple research sites for better generalizability, and explore the moderating effects of vocabulary fluency in diverse L2 learning contexts.

The study's generalizability may be limited by its single-site design and the specific aspects of vocabulary depth assessed. The receptive vocabulary depth test included only word parts, multiple meanings, and collocations, which might not fully represent the multifaceted nature of vocabulary depth. Future research could incorporate a broader range of vocabulary depth aspects and employ a multi-site design to enhance the generalizability of the findings.