Effects of text length on lexical diversity measures: Using short texts with less than 200 tokens

Despite the importance of lexical diversity (LD) in L2 speaking and writing performance, LD assessment measures are known to be affected by the number of words analyzed in the text. This study aims to identify LD measures that are less affected by text length and can be used for the analysis of short L2 texts (50-200 tokens). We compared the type-token ratio, Guiraud index, Maas, measure of textual lexical diversity (MTLD), D, and HD-D to assess their degree of susceptibility to text length. Spoken texts of 200 tokens from 38 L2 English learners at the lower-intermediate-level were divided into segments of 50-200 tokens and the text length impact was examined. We found that MTLD was less affected by text length across most ranges, but was somewhat affected across 50 to 150 and 50 to 200 tokens. We further observed low correlations between equal-sized texts for up to 100 tokens. These results suggest that MTLD can be used with texts of more than 100 tokens and compared between 100- and 200-token texts. We also showed that D and HD-D produced similar results for texts, thus indicating that D and HD-D are comparable.