Table 4.4 Differences in lexical variation (MSR-D).11
1 Introduction
1.1    Research Background
In general, there are three dimensions of language standards: fluency, accuracy and sophistication. In second language acquisition (L2 acquisition), the three dimensions play a very important role in this learning process. Among various skills in L2 acquisition, such as listening, reading and so on, writing is one of the most important and practical competences.
Since the 1980s, research on vocabulary in L2 writing has become a hot topic and has caught much interest from experts and scholars in such fields. With the development and application of various lexical measuring tools and lexical analysis software, research on vocabulary in L2 writing becomes more scientific and easier. The help of technology makes it possible to open the width and to dig the depth of lexical research.
In this paper, lexical richness will be discussed, which is a part of the sophistication of the three dimensions mentioned above which are also very important in the progress of writing. In L2 writing, there are many factors which determine the quality of an essay, lexical richness is one of them and has gathered more and more attention among scholars all over the world these years.
1.2    Significance of this research
Vocabulary to an essay is the same as bricks to a building. Lexical richness, as an important measurement of the quality of an essay, values a lot in the process of undergraduates’ L2 writing. More research on this topic gives university teachers more suggestions and inspiration on the teaching of L2 writing and L2 acquisition while helping undergraduates in self-learning, which can be very helpful to improve their L2 writing skills.
Theories will serve practice eventually. It is necessary to be aware of the strengths and weaknesses in students’ L2 writing through endless research and analysis, which can be regarded as a guidance for university teachers to come up with new methods in teaching and for students to know how to improve the writing skills of their own. By way of numerous research data on vocabulary in L2 writing which becomes more comprehensive and more practical, the achievements will become a kind of precious textbook in practice and will leave much more space and possibility for students to write compositions of high quality.
2 Literature Review
2.1 Previous Studies of Lexical Richness on L2 Writing
2.1.1 Previous Studies Aboard
Generally, researchers introduced three main methods for measuring lexical richness. First, Laufer and Nation (1995) took lexical originality, lexical density, lexical sophistication and lexical variation as four dimensions to measure lexical richness. Then, Engber (1995) added lexical error into its measurement range, developing the measuring pattern into lexical variation, error-free lexical variation, lexical error and lexical density. At last, however, Read (2000) found out that in the background of L2 writing, lexical originality is not suitable to evaluate the development of L2 learners’ lexical competence and gave 4 new aspects to measure lexical richness, which were lexical variation (type/token ratio), lexical sophistication, lexical density, and a small number of lexical error.
2.1.2 Previous Studies in China
In China, research on lexical richness has also got much achievement, such as Liu Donghong and Wan Lifang who are two representative scholars in this field.
Liu Donghong (2003) discussed the relationship between the quality of an essay and productive vocabulary. This kind of effect of productive vocabulary on the quality of an essay is not direct, it influences the writing length indirectly instead. Productive vocabulary, which is much smaller than receptive vocabulary, plays a very important role in the construction of an essay for that it effects lexical richness in L2 writing, for example, students with a larger vocabulary size prefer to use less K1 words and more sophisticated words. 不同英语写作水平学生议论文写作词汇丰富性差异研究(2):http://www.youerw.com/yingyu/lunwen_31277.html