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(1995) considered that lexical richness include  lexical  variation  with  error,  lexical  variation  without  error,  percentage  of lexical error and lexical density. Laufer (1991), Laufer and Nation (1995) defined four dimensions  of  lexical  richness,  namely,  lexical  variation,  lexical  density,  lexical sophistication and lexical originality. While in the context of second language writing, Read (2000) pointed out that lexical originality could not evaluate the development of lexical performance. He took error into consideration and modified Laufer and Nation (1995)  categorization  by  defining  lexical  richness  as  a  superordinate  term  for  the effective use of vocabulary in good writing. It is composed of lexical variation, lexical sophistication,  lexical  density  and  a  low  number  of  errors.  In  this  model,  lexical richness can be measured from four dimensions: lexical individuality, lexical density, lexical variation and lexical sophistication.  
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2.2   Measurement Indexes for Lexical Richness 
Lexical richness is a superordinate term which can reflect the whole situation of vocabulary use in second language writings. As mentioned above, it can be reflected by  different  specific  features  according  to  different  definitions.  As  a  result,  the measurement  indexes  also  vary  a  lot  in  different  studies.  Different  researchers  have used a large number of different measurement indexes because they tend to approach lexical  richness  from  many  different  perspectives  in  search  of  the  valid  and  reliable measurement indexes for language learners’ lexical richness in a text. In this study, the measurement  indexes  are  chosen  as  lexical  sophistication,  lexical  variation,  lexical density and lexical errors according to Read’s (2000) theoretical framework. Lexical  variation  refers  to  the  range  of  a  learner’s  vocabulary  as  displayed  in language  use.  It  is  also  called  lexical  diversity  or  lexical  range  by  some  researchers. (e.g.  Crystal,  1982;  Malvern  et  al.,  2004;  Yu,  2010)  Read  (2000)  defined  lexical variation  as  a  variety  of  different  words  rather  than  a  limited  number  of  words  used repetitively  in  writing.  He  also  points  out  that  Lexical  variation  is  reflected  by  the type-token ratio of the lexical words in the text. The “types” here refer to the different lexical words used in the text, while the “tokens” are all the lexical words used in the text including the repetitions of words that are used more than once.  
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Chapter Three   Methodology ..... 16 
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