Size and strength: do we need both to measure vocabulary knowledge?

This article describes the development and validation of a test of vocabulary size and strength. The rst part of the article sets out the theoretical rationale for the test, and describes how the size and strength constructs have been conceptualized and operationalized. The second part of the article focusses on the process of test validation, which involved the testing of the hypotheses implicit in the test design, using both unidimensional and multifaceted Rasch analyses. Possible applications for the test include determining the status of a learner’s vocabulary development as well as screening and placement. A model for administering the test in computer adaptive mode is also proposed. The study has implications both for the design and delivery of this test as well as for theories of vocabulary acquisition.