Type-Token Ratio

The type-token ratio (TTR) is the oldest and most widely used measure of lexical diversity: the number of distinct word types in a text divided by the total number of word tokens. A text in which few words repeat yields a TTR near 1, while a text that recycles a small vocabulary yields a TTR near 0. Despite its intuitive appeal and trivial computation, the raw ratio is severely confounded by text length, which has motivated a long line of length-correcting transformations and, ultimately, the more robust indices that have largely superseded it for serious comparison.