Type versus Token or Type–Token Ratio (TTR) is used in the fields of linguistics and Speech–Language pathology as an estimate of the lexical diversity of a speaker’s expressive vocabulary. It accomplishes this by examining the relationship between the total number of different words (NDW) used and the total number of words used. Views on quantifying lexical diversity favor the use of other measures with disordered language, but TTR has been applied to children’s expressive vocabulary to differentiate typical from impaired language development. This entry provides an overview of how TTR works and how parts of speech can be used to calculate TTR.

How TTR Works

TTR was first described in the work of Mildred Templin in the mid-1950s in data collected from 3- to 8-year-olds in 1:2 ...

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