学位論文の要旨
Exploring the Role of Vocabulary in Writing: Predicting Lexical論 文 題 目 Diversity

Scores,Differentiating

Writing

Proficiency,andInvestigating Vocabulary Knowledge Development Over Time氏

名 Yajie Li
This dissertation investigates the role of vocabulary knowledge in L2 writing:the extent to which vocabulary knowledge scores can predict vocabulary use in writing
activities for participants with different proficiency levels; how vocabulary knowledge
scores can distinguish participant writing scores; and to what extent vocabularyknowledge scores and written production can track acquired vocabulary knowledge.
To explore these questions, I conducted four experiments (three cross-sectional andone longitudinal) and distributed a range of vocabulary tasks to help determine
participants’ vocabulary knowledge. Nation’s framework of vocabulary knowledge(1990, 2001, 2013) divides vocabulary knowledge into receptive and productivedimensions. Receptive vocabulary knowledge requires participants to understand theform and meaning of words, and productive vocabulary knowledge demands
participants to produce words. We can use vocabulary tasks as effective tools to test
participants’ vocabulary knowledge. Lexical diversity is one such effective tool tomeasure the variety of different words used in actual written texts or spoken
production. By using lexical diversity measurements, it is possible to estimate

vocabulary knowledge in writing use, writing competence, and overall language
proficiency levels (e.g., Engber, 1995; Lu, 2012; Olinghouse & Leaird, 2009; Olinghouse& Wilson, 2013; Treffers-Daller, 2013; Treffers-Daller et al., 2018; Vidal & Jarvis, 2020;
Yu, 2010).
The first experimental chapter partially replicates Treffers-Daller et al. (2018)
and explores potential relationships between vocabulary tasks and L2 written
production for participants at the Common European Framework of Reference (CEFR)
A2 level (Council of Europe, 2001). It examines whether vocabulary scores can predict
participants’ vocabulary in writing use with 29 L1 Chinese participants. I gave
participants four vocabulary knowledge tasks: Lex30, a task based on word association(Meara & Fitzpatrick, 2000); G_Lex, a single-word gap-fill task (Fitzpatrick & Clenton,2017); the Productive Vocabulary Levels Test (the PVLT), a sentence completion task(Laufer & Nation, 1999); the Vocabulary Levels Test (the VLT), a form-meaning
matching task (Nation, 1983; Schmitt, 2000) assessing receptive vocabularyknowledge; and one writing topic (see Appendix A for specific examples of Lex30,
G_Lex, the PVLT, the VLT, and writing topic).
The second experimental chapter focuses on productive vocabulary knowledge
tasks and investigates potential relationships between productive vocabulary tasks

and L2 written production for participants at CEFR levels B1 to C1. This experimentexamines 91 L1 Japanese participants with higher proficiency levels. Considering thatwriting is a productive skill and that the PVLT task also accesses facets of receptive
vocabulary knowledge (Edmonds et al., 2022; Webb, 2008), I gave participants three
productive vocabulary tasks (Lex30, G_Lex, the PVLT) and one IELTS writing topic(see Appendix B for sample responses of Lex30, G_Lex, the PVLT, and IELTS writing).
The third experimental chapter examines how productive vocabulary tasks
can differentiate between IELTS writing scores. 63 L1 Japanese speakers and 35 L1
French speakers participated in this experiment. All participants finished the three
productive vocabulary tasks (Lex30, G_Lex, and the PVLT) and two IELTS writingtopics (see Appendix E for sample responses of Lex30, G_Lex, the PVLT, and IELTS
writing). Qualified IELTS raters marked all the writing samples based on the IELTS
writing rubric (see Appendix C for IELTS writing band descriptors). I divided allparticipants from the two different language backgrounds into different proficiency
groups based on their IELTS writing scores.
The fourth experimental chapter explores how productive vocabularyknowledge task scores and lexical diversity measure scores relate over a short study
period. It investigates whether participants’ vocabulary knowledge and lexicaldiversity scores can improve through a pre- and post-test design over a short-term
intervention (approximately 12 weeks). Participants from a single language
background (L1 Japanese participants, N=51) with similar proficiency levels joined
the current experiment. I used two versions of three productive vocabulary knowledgetasks (Lex30, G_Lex, and the PVLT) and two IELTS writing topics (with different
question prompts at each test time) at the beginning and the end of the study period(see Appendix F for sample responses of vocabulary tasks and IELTS writing at testingtime one and testing time two). I gave all participants the same vocabulary lists (2KNew General Service List [NGSL]) to learn.
In a partial replication of Treffers-Daller et al.’s (2018) study, I use the lemma,
which comprises ‘a headword and its inflected forms’ (Nation, 2016, 2022), as wordunit both for responses from vocabulary tasks and writing samples in my firstexperiment. A research gap in Treffers-Daller et al.’s study left using the flemma,
which comprises ‘a headword and inflected forms of different parts of speech’ (Nation,2016, 2022) as a word unit unexplored, I have used the flemma as a word counting
unit for my second, third, and fourth experiments.
The findings from the four experimental chapters raise several key issues todiscuss and explore further: (i) disparities in accessing vocabulary knowledge used inwritten production, as evidenced by vocabulary knowledge measures: vocabularyknowledge measures differ in task features and task embeddedness; (ii) measuring
vocabulary knowledge can differentiate levels of proficiency in IELTS writing; (iii)selecting appropriate measures of lexical diversity depends on the specific researchquestion or goal, as different measures may have different strengths and limitations.
Traditional lexical diversity measure scores show greater accuracy with vocabularyknowledge scores in writing use, whereas the more recently devised lexical diversity
measures show better performance in tracking vocabulary knowledge development inwritten production; (iv) G_Lex shows greater power in tracking vocabulary knowledge
improvement than the PVLT and Lex30; and, (v) using online flashcards learning with
2K NGSL lemma-based word lists offers an effective means to improve vocabularyknowledge and vocabulary in writing use.
In conclusion, I hope the issues identified and investigated regarding thedynamic relationship between vocabulary knowledge and written production cansupport future research. The findings’ implications are significant for L2 writing classand vocabulary knowledge assessment.