Lexical richness in the spontaneous speech of bilinguals

The focus of the present paper is on the measurement of lexical richness. Lexical richness is often measured either by the traditional type-token ratio (TTR) or by its square root variant, the index of Guiraud. The disadvantages of these measures, especially those of the TTR, are well-known. In this paper we propose two measures (Advanced TTR and Guiraud Advanced) that have clear advantages over the traditional measures. These two measures combine characteristics of type/token related measures with the notion of different layers of frequency/productivity in the lexicon (see Laufer and Nation 1995). We computed indices for the lexical items used in an oral text production task by two groups of Turkish-German bilinguals. One group has a German dominant bilingual competence; the other group consists of Turkish dominant bilinguals. It will be shown that the proposed measures for advanced lexical richness trace the characteristics of the bilingual profiles of the groups of subjects better than the traditional measures. Since the two languages involved in this study are typologically quite different, the additional technique of standardizing scores (z scores) was required to draw comparisons between the two languages. The conclusion is that the two proposed indices of advanced lexical richness, and especially the Guiraud Advanced, yield the clearest results. The new measures can be readily computed and are useful in the context of linguistic research as well as in classroom settings.