词汇多样性 Lexical Diversity
Lexical diversity refers to the variety of unique words (types) that occur in a text in relation to the total number of words (tokens). When the number of word types is equal to the total number of words (tokens), then all of the words are different. In that case, lexical diversity is at a maximum, and the text is likely to be either very low in cohesion or very short. A high number of different words in a text indicates that new words need to be integrated into the discourse context. By contrast, lexical diversity is lower (and cohesion is higher) when more words are used multiple times across the text.
词汇多样性是指文本中出现的独特词语（类型，即type）的种类与词语（标记，即token）总数的关系。当单词类型的数量等于单词（词块）总数时，所有的单词都是不同的。在这种情况下，词汇多样性达到最大值，文本的衔接力可能很低。文本中不同词的数量多，说明新词需要融入话语语境。相比之下，当文本中多次使用较多词语时，词汇多样性较低（衔接力较高）。