Estimating the Vocabulary Size of L1 Spanish ESP Learners and the Vocabulary Load of Medical Textbooks

The main goal of this research on the vocabulary load of medical textbooks is to use a corpus-based approach to investigate the number of words learners of English for Specific Purposes (ESP) need to meet the lexical demands of medical textbooks written in English, and achieve a good reading comprehension of such texts. This thesis explores the relationship between vocabulary size of prospective learners of ESP in two Spanish medium universities in Venezuela, and the vocabulary load of medical textbooks. The two main variables considered to calculate the vocabulary load of medical textbooks were the vocabulary sizes of ESP undergraduate students, and the lexical text coverage of medical textbooks. In order to determine the vocabulary size of ESP learners, a monolingual version of Nation and Beglar’s (2007) Vocabulary Size Test (VST) and a Spanish bilingual version of the same test, which was translated for the purpose of the present study, were administered to a group of 408 English as a foreign language (EFL) learners who are speakers of Spanish as a first language (L1). For determining the lexical text coverage of medical textbooks, a written medical (med1) corpus of 5.4 million tokens, and a general comparison corpus of the same size were used. The lexical text coverage was estimated in two ways, with the help of existing word lists such as the General Service list (GSL; West, 1953), the Academic Word list (AWL; Coxhead, 2000), the Pilot Science List (PSL; Coxhead and Hirsh, 2007), and with the help of the British National Corpus/Corpus of Contemporary American English (BNC/COCA; Nation, 2012) word family lists. Additionally, medical words across the high, mid and low-frequency bands were identified using a two-level semantic rating scale designed for this purpose, and a set of over thirty 1,000 medical word lists developed. The new medical word lists created using the med1 corpus were then validated on a different medical corpus (i.e., the med2 corpus) of a similar size (5.8 million tokens). The major finding of this thesis was that in order to reach the 98% lexical threshold required to achieve optimal reading comprehension of medical textbooks written in English, besides the top 3,000 most frequent word families of the English language, ESP learners doing medical studies would need to know at least 26,000 words related to the medical field. Moreover, this research found that when adding medical words from the existing word lists (e.g., GSL, AWL, Pilot Science List, and BNC/COCA lists) to the new medical word lists created here, the overall coverage of medical words gets close to 37% of the running words in the medical text. In relation to the vocabulary size of the EFL learners tested, this research determined: (1) the average vocabulary size of the Spanish as a first language (L1) ESP students taking the VST which was around 6,000 word families, and (2) the point at which it becomes more efficient for the medical students to focus on medical words rather than general words (e.g., knowledge of the 5,000 most frequent families). The results of this research placed particular emphasis on the medical words that ESP students meet in medical textbooks, but may not learn through existing general and academic word lists.