1. 研究目的与意义（文献综述包含参考文献）

1. Introduction1.1Background of the research Test for English Majors-Band 8 (TEM-8) has been sponsored by The National Administry Committee on Teaching English Language to Majors in Higher Education under The Ministry of Education since 1991. It is an English proficiency test for senior students majoring in English and related majors in China. In terms of English proficiency certificates, tem-8 is the highest level within the scope of the domestic examination. TEM-8 consists of five sections: listening comprehension, proof reading and error correction, reading comprehension, translation, and writing. Among them, reading comprehension section accounts for 30% of the total score, the highest proportion among the five sections. Therefore, researchers have long explored the teaching of English reading for English majors. Textbooks play an essential role in ensuring teaching quality in college and university English education. It is also the premise of achieving the teaching content and realizing the teaching goal. The quality of a textbook is a decisive factor affecting English teaching and learning (Huang, 2011). At present, although the market of compiling and publishing English textbooks is booming, empirical English textbooks evaluation research is limited.There is no doubt that vocabulary is the most important factor restricting foreign language learning efficiency. Vocabulary is the foundation of English, which runs through the whole process of English learning. Especially for English reading, vocabulary plays a decisive role. It determines not only the reading speed but also the comprehension of the texts. As vocabulary is a key factor affecting learners reading comprehension, what is the relationship between vocabulary in reading textbooks and that of reading comprehension in TEM 8. 1.2Purposes of the researchLexical richness is about the quality of vocabulary in a language sample. A sophisticated, diverse, and accurate lexical contribution to texts enhances writing quality and mirrors the learners writing proficiency (Laufer Read, 2000). Therefore, lexical richness is a crucial aspect in the quality of texts. This paper will compare the lexical richness of reading texts in the Advanced English textbooks with that of the TEM-8 reading materials. Theoretically, it can enrich the research in the field of lexical richness and provide a feasible research paradigm for future researchers. In practice, this paper provides some references for vocabulary teaching and learning in English reading class. 1.3 Organization of the researchThis paper consists of five parts. The first chapter is the general introduction, which describes the research background, research purpose, and the organization of the research. In chapter two, there is an overview of the literature, including the definition of lexical richness, relevant empirical studies on lexical richness and reading comprehension texts, and research gaps. Chapter three depicts the specific methodology of this research, introducing the research questions, research subjects, and the measurement of lexical richness. Chapter four reports the key findings based on the analysis of the research data and a detailed discussion of the major findings. This thesis ends with a summary of the major findings, the implications, and limitations and suggestions for future research in Chapter Five.2. Literature ReviewIn this chapter, the relative literature is reviewed in three parts: the definition of lexical richness, empirical studies on lexical richness, and reading comprehension texts. Finally, research gaps are presented.2.1 Lexical RichnessLexical richness is a reliable terminology for vocabulary knowledge which has been considered as a significant indicator of the quality of L2 writing (Nation, 2013). As a comprehensive term covering different dimensions, researchers have various classifications of lexical richness. According to Linnarud (1986), lexical richness is evaluated from four dimensions: lexical density, lexical variation, lexical sophistication, and lexical individuality. 2.1.1 Lexical DensityUre (1971) first proposes the term lexical density, which is described as the percentage of content words (also known as lexical items) in a text. Halliday (1985) regards lexical density as a typical complexity of written language. Read (2000) also proposes that lexical density is one of the characteristics of written discourse. Biber and Gray (2010) emphasize that professional readers can immediately get rich information from shorter and more concise texts in these styles. 2.1.2 Lexical Variation Lexical variation refers to the use of different words by learners in language expression in order to avoid repeated use of certain words, also known as lexical diversity (Wang, 2017). Read (2000) investigates the complexity of learners vocabulary by calculating the proportion of complex word families in the total word family according to the word frequency level to which the word belongs. 2.1.3 Lexical SophisticationAccording to the definition given by Read (2000), lexical sophistication refers to the portion of relatively unusual or advanced words correctly spelled in the total number of words. The unusual or advanced words here refer to low-frequency words. Low-frequency words are presented and used relatively infrequently and are not easy to learn, so the number of low-frequency words can explain students degree of language learning to some extent.2.1.4 Lexical IndividualityAccording to Laufer Nation (1995), lexical individuality refers to the ratio of words used by a participant that is not used by other participants in the same group, divided by the total number of words used by the participant. Lexical individuality interprets the personal qualities and traits, which refers to the proportion for which personal vocabulary accounts for in an essay, in a better way. (Read, 2002)2.2 Previous Empirical Study Since the beginning of the 20th century, many studies on this issue have aroused great interest from foreign researchers. Initially, lexical richness is measured as a differentiating factor in the quality of L1 writing (Grobe, 1981). Later, the term is applied to second language studies. For example, Linnarud (1986) conducts a comparative study on the differences between Swedish and British students in English writing. The results show that British students perform better in English writing than Swedish students. Lemmouh (2008) looks into the relationship between lexical richness and composition scores, academic performance, and vocabulary knowledge by analyzing the compositions written by 37 high-level English learners at Swiss universities. The research finds that there is a correlation between the use of advanced vocabulary and academic performance. The more advanced vocabulary is used, the higher the academic performance is. Dhani Aldila Putra and Iwa Lukmana (2017) investigate lexical richness progression in the reading texts of English textbooks published for senior high school students in Indonesia. The results show that the lexical density and lexical variation across the textbooks are found to have a consistent progression from one grade level to another of which the direction is positive.The research on the lexical richness of reading tests in China is still in its infancy, and the research methods and standards are different. Bao (2008) finds in a multidimensional study on the richness of the second language written vocabulary of 150 college students that word variation is related to text length. Jiang Han (2018) use the Coh-Metrix tool to make a comparative analysis of the difficulty of 163 reading texts of CET-6, TOEFL, and IELTS in recent years. Their research shows that the difficulty of CET-6 is lower than that of TOEFL and IELTS in reading. Gu Guan (2003) use the Flesch Reading Easy formula to conduct a sample study on the readability of CET-4 and CET-6 Reading tests and college English reading materials. The results of this study show that the CET 4 and CET 6 reading tests follow the readability principle well. However, college English reading textbooks should be improved in this aspect. 2.3 Research GapsAt present, there is abundant research on lexical richness. But most of them focus on writing and little on reading comprehension. Moreover, there are few studies on the comparison between reading comprehension tests and textbooks. In particular, there are few comparative studies on the TEM-8 reading comprehension test and Advanced English textbooks.

2. 研究的基本内容、问题解决措施及方案

Research Design and MethodIn this chapter, we will discuss the research questions, research subjects, and research tools of this study. We will analyze the lexical richness of texts in Advanced English textbooks and TEM-8 reading tests in terms of LD, LV, LS, and LI.3.1 Research QuestionsThis study is to compare lexical richness of texts in college English reading textbooks with that in the TEM8 reading section to understand the difference in lexical richness between what we teach and what we test. We mainly try to explore and find answers to the following four research questions: 1. What is the difference in lexical density between Advanced English textbooks and TEM-8 reading comprehension texts?2. What are the differences in lexical variation between Advanced English textbooks and TEM-8 reading comprehension texts?3. What is the difference in lexical sophistication between Advanced English textbooks and TEM-8 reading comprehension texts?4. What is the difference in lexical individuality between Advanced English textbooks and TEM-8 reading comprehension texts?3.2 Research SubjectsIn this paper, a self-built comparable corpus is used for empirical research. The corpus consists of two parts: TEM8 reading discourse corpus and Advanced English textbook corpus. The first part used 15 reading comprehension texts of TEM-8 since the reform in 2016 (TEM-8 was canceled in 2020 due to the COVID-19). The vocabulary of the TEM-8 reading comprehension test is about 6500 words. The second group is Advanced English (the third edition) and Advanced English (the revised Edition) (Volume 2), which are compulsory textbooks for junior and senior English majors in Nanjing Tech University. There are 30 basic texts in two volumes. The vocabulary of the Advanced English textbooks is close to 60000 words. The researchers saved each text as a plain text file and unified the format of the two groups of texts. Including deleting the title of the textbook text and the Chinese definition of the superkey words in the test text and unifying punctuation marks into English input, etc.3.3 Research Tools 3.3.1 Lexical DensityLexical density measures the proportion of content words in the whole text and examines the information content of the text. This study uses the following statistical formula: content word repetition is allowed, that is, information repetition is allowed, content words with different inflected forms are treated as different types (only the correct types are considered). The Lexical density is calculated by R software. 3.2.2 Lexical VariationLexical variation is measured by the type/token ratio. Types are words that are used in the text. Lexical variation is processed through R software too. The package called koRpus is of multitudinous functions to analyze texts. 3.2.3 Lexical Sophistication Lexical sophistication measures the proportion of low-frequency words in a text. The lexical sophistication value is the ratio of the total number of low-frequency word types with truncated tails (only the correct word positions are considered) to the total length of the text. 3.2.4 Lexical IndividualityLexical individuality is the ratio of the total number of correct words (in terms of the lexeme, i.e. word types truncated) that are used alone in a text in a group to the total length of the text. This study used an online tail chipping processor (lemmatizer).