Type/Token Ratios: what do they really tell us?

Abstract

Type/Token Ratios have been extensively used in child language research as an index of lexical diversity. This paper shows that the measure has frequently failed to discriminate between children at widely different stages of language development, and that the ratio may in fact fall as children get older. It is suggested here that such effects are caused by a negative, though non-linear, relationship between sample size (i.e. number of tokens) and Type/Token Ratio. Effects of open and closed class items are considered and an alternative Verbal Diversity measure is examined. Standardization of the number of tokens before computing Type/Token Ratios is recommended.