The relationship between vocabulary size and depth for ESP/EAP learners

Vocabulary knowledge occupies an important position in language learning. This study investigates the relationship between vocabulary size and depth for Iranian learners of English for specific/academic purposes (ESP/EAP). The participants include 112 ESP graduate students at a university in Iran. The findings from linear regression analyses show that, overall, VLT (size test) and WAT (depth test) have a great deal of common shared variance for these participants (R2 = .746). However, when they were divided into low and high proficiency groups, based on whether the participants mastered the most frequent 2000 words in VLT, a substantial amount of shared variance was shown for the low group (R2 = .464) and a much higher one for the high group (R2 = .804). The findings suggest that vocabulary size and depth might be accounted for by the same factors, especially as the learners’ proficiency increases.