<p>Understanding academic spoken English is challenging for second language (L2) learners at English-medium universities. A lack of vocabulary is a major reason for this difficulty. To help these learners overcome this challenge, it is important to examine the nature of vocabulary in academic spoken English. This thesis presents three linked studies which were conducted to address this need. Study 1 examined the lexical coverage in nine spoken and nine written corpora of four well-known general high-frequency word lists: West’s (1953) General Service List (GSL), Nation’s (2006) BNC2000, Nation’s (2012) BNC/COCA2000, and Brezina and Gablasova’s (2015) New-GSL. Study 2 further compared the BNC/COCA2000 and the New-GSL, which had the highest coverage in Study 1. It involved 25 English first language (L1) teachers, 26 Vietnamese L1 teachers, 27 various L1 teachers, and 275 Vietnamese English as a Foreign Language learners. The teachers completed 10 surveys in which they rated the usefulness of 973 non-overlapping items between the BNC/COCA2000 and the New-GSL for their learners in a five-point Likert scale. The learners took the Vocabulary Levels Test (Nation, 1983, 1990; Schmitt, Schmitt, & Clapham, 2001), and 15 Yes/No tests which measured their knowledge of the 973 words. Study 3 involved compiling two academic spoken corpora, one academic written corpus, and one non-academic spoken corpus. Each contains approximately 13-million running words. The academic spoken corpora contained four equally-sized sub-corpora. From the first academic spoken corpus, 1,741 word families were selected for the Academic Spoken Word List (ASWL). The coverage of the ASWL and the BNC/COCA2000 in the four corpora and the potential coverage of the ASWL for learners of different vocabulary levels were determined. Six main findings were drawn from these studies. First, in the first academic spoken corpus, the ASWL and its levels had slightly higher coverage in certain disciplinary sub-corpora than in the others. Yet, the list provided around 90% coverage of each sub-corpus. It helps learners to achieve 92%-96% coverage of academic speech depending on their levels. Second, the BNC/COCA2000 is the most suitable general high-frequency word list for L2 learners from the perspectives of corpus linguistics, teachers, and learners. It provided higher coverage than the GSL and the BNC2000, and had more words known by learners and perceived as being useful by teachers than the New-GSL. Third, general high-frequency words, especially the most frequent 1,000 words, provided much higher coverage in spoken corpora than written corpora in both academic and non-academic discourse. Fourth, despite the importance of general high-frequency words, a reasonable proportion of the learners had insufficient knowledge of these words, which highlights the importance of a word list which is adaptable to learners’ proficiency like the ASWL. Fifth, lexical coverage had significant but small correlations with teacher perception of word usefulness and learner vocabulary knowledge. Sixth, the Vietnamese L1 teachers had the highest correlation between the teacher ratings of word usefulness and the learner vocabulary knowledge. Next came the various L1 teachers, and then the English L1 teachers. This thesis also provides theoretical, pedagogical, and methodological implications of these findings so that L2 learners can gain better support in their vocabulary development and achieve better comprehension of academic spoken English.</p>
Co-Occurrence Network of High-Frequency Words in the Bioinformatics Literature: Structural Characteristics and Evolution
