Validated yes/no vocabulary tests that measure bilinguals’ language proficiency based on vocabulary knowledge have been widely used in psycholinguistic research. However, it is unclear what aspects of test takers’ vocabulary knowledge are employed in these tests, which makes the interpretation of their scores problematic. The present study investigated the contribution of bilinguals’ form-meaning knowledge to their item accuracy on a Malay yes/no vocabulary test. Word knowledge of Malay first- (N = 80) and second-language (N = 80) speakers were assessed using yes/no, meaning recognition, form recognition, meaning recall and form recall tests. The findings revealed that 59% of the variance in the yes/no vocabulary test score was explained by the accuracy of the meaning recognition, form recognition and meaning recall tests. Importantly, the item analysis indicated that yes/no vocabulary tests assess primarily knowledge of form recognition, supporting its use as a lexical proficiency measure to estimate bilinguals’ receptive language proficiency.
