The present study aimed to validate a 70-item Korean bilingual version of the Vocabulary Size Test (VST) using Rasch modeling. The goal was to assess the applicability of this Korean version of the VST for Korean learners of English in an English as a foreign language (EFL) context by examining validity evidence based on Messick’s framework. Specifically, the study focused on the content, substantive, and external aspects of construct validity. However, the findings provided weak evidence supporting the utility of the VST as a measure of receptive vocabulary for Korean EFL learners. The test was deemed too easy and lacked the ability to effectively differentiate among varying levels of second language proficiency, with many test items exhibiting unexpected behavior. Additionally, the VST showed a weak correlation with another measure of second language proficiency. In light of these findings, the study offers specific recommendations for improving the test's validity and usefulness.

1. INTRODUCTION
2. LITERATURE REVIEW
    2.1. Validation Work of Bilingual Versions of the VST
    2.2. Korean Bilingual Versions of VST
3. RESEARCH QUESTIONS
4. METHODOLOGY
    4.1. Participants and Data
    4.2. Instruments
    4.3. Analysis
5. RESULTS
    5.1. Assessment of Item Discrimination for Distinguishing High and LowPerformers (RQ 1)
    5.2. Assessment of Item Spread and Fit to the Rasch Model (RQ 2)
    5.3. Alignment of Item Difficulty Estimates with Word Frequency Levels inthe BNC List (RQ 3)
    5.4. Comparison of Korean VST Scores with Other Measures of EnglishProficiency (RQ 4)
6. DISCUSSION
7. CONCLUSIONS
REFERENCES
APPENDIX

• Hae In Park(Assistant Professor, Department of Applied English Linguistics and Translation Studies, Kyung Hee University; 26, Kyungheedae-ro, Dongdaemun-gu, Seoul, 02447, South Korea)