An Investigation into the Roles of Guessing and Partial Knowledge in the Vocabulary Size Test

Although an accurate measure of vocabulary size is integral to understanding the proficiency of language learners, the validity of multiple-choice (M/C) vocabulary tests to determine this has been questioned due to users guessing correct answers which inflates scores. In this paper the nature of guessing and partial knowledge used when taking the Vocabulary Size Test (VST) is examined. The analysis evaluates the thought processes of test takers through think-aloud protocols and self-reports. This provides a taxonomy of seven types of guesses used by learners while taking the VST and measures the frequency of their occurrence. Based on qualitative coding, guesses are investigated to determine if they exhibit partial word knowledge which is relevant to the test construct. The findings suggest that both guesses resulting from the use of partial knowledge and random guesses are included in estimates and this has a detrimental effect on test accuracy. The paper concludes that the VST does not provide an accurate measure of the vocabulary necessary for reading due to guessing and the meaning-recognition format. It also suggests that the role of partial knowledge should be considered when producing more sophisticated vocabulary tests in the future.