Abstract
The present study attempts to produce a revised version of the Mochizuki Vocabulary Size Test (Mochizuki, 1998). There is room for further improvement of this test, though it has been used as a reliable vocabulary size test for Japanese learners of English. The present study employs FACETS, which is Item Response Theory software, and identifies 21 items to be discarded. Then more suitable new items are chosen based on the JACET List of 8000 Basic Words (JACET, 2003). It was found that the new version is as reliable as the original VST and moreover, the modified version has no misfit items.
