The relationship between language proficiency and Iranian EFL learners' knowledge of vocabulary depth versus vocabulary breadth

The present study intended to examine the relationship among language proficiency, vocabulary depth, and vocabulary breadth of Iranian EFL learners. To achieve this end, 80 students at Upper-and Lower-Intermediate levels were randomly chosen from the population of ShahidBeheshti School in Khoramabad as participants of this study. Firstly, an Oxford Placement test (OPT) was administered to determine the subjects' level of proficiency. Each group at Upper-and Lower-Intermediate levels received Nation 2000, 3000, and 5000 tests to determine the vocabulary size of the learners. Two weeks later, Vocabulary Knowledge Scale (VKS) was used in order to determine the learners' vocabulary depth. The results of the correlation coefficients indicated that there was a significant relationship between vocabulary breadth, vocabulary depth, and language proficiency of the learners. In addition, the results of multiple regressions revealed that vocabulary depth is a better predictor of learners' language proficiency than of vocabulary breadth.