The purpose of this study was to construct two Japanese language ability scales, namely, vocabulary and Chinese character recognition, at senior high school level. Four tests were constructed from the original items and administered to about 27,000 Japanese high school students for each scale. The statistical item analysis showed that 242vocabulary items and 413 Chinese character items could be used for the item response theoretic analysis. IRT analysis of the item responses was carried out separately for each test and the estimated item parameters were equated utilizing the anchor items included in all the tests.
