Reliable Measure of Written Receptive Vocabulary Size: Using the L2 Depth of Vocabulary Knowledge as a Yardstick

This study investigates the correlations between the three measures of written receptive vocabulary size and second language (L2) depth of vocabulary knowledge to find the most reliable test of vocabulary size. Moreover, the corresponding relationship is examined for the higher and lower word-frequency bands of the three tests to find whether the correlation between the two constructs differs as a function of frequency level and task format. In so doing, Vocabulary Levels Test (VLT), the monolingual and bilingual Persian versions of the Vocabulary Size Test (VST), and Word Associates Test (WAT) were administered to 122 high-proficient undergraduate English as a foreign language (EFL) learners. Results of Pearson correlations and linear regression analyses indicated that (a) the VLT had the highest correlation with the participants’ scores on the WAT; (b) although all the three tests of vocabulary size could significantly predict L2 depth of vocabulary knowledge, the VLT was the strongest predictor; (c) the higher word-frequency levels of the three VSTs in general, and the VLT in particular, were more predictive of L2 vocabulary depth; and (d) the 3,000-word-frequency level of the VLT, in particular, had the highest contribution to the performance on the WAT. The overall findings point to the superiority of the VLT among the three measures of vocabulary size.