Although lexical diversity is often used as a measure of productive proficiency (e.g., as an aspect of lexical complexity) in SLA studies involving oral tasks, relatively little research has been conducted to support the reliability and/or validity of these indices in spoken contexts. Furthermore, SLA researchers commonly use indices of lexical diversity such as Root TTR (Guiraud’s index) and D (vocd-D and HD-D) that have been preliminarily shown to lack reliability in spoken L2 contexts and/or have been consistently shown to lack reliability in written L2 contexts. In this study, we empirically evaluate lexical diversity indices with respect to two aspects of reliability (text-length independence and across-task stability) and one aspect of validity (relationship with proficiency scores). The results indicated that neither Root TTR nor D is reliable across different text lengths. However, support for the reliability and validity of optimized versions of MATTR and MTLD was found.

尽管在涉及口语任务的 SLA 研究中，词汇多样性经常被用作生产熟练程度的衡量标准（例如，作为词汇复杂性的一个方面），但支持这些指标在口语环境中的可靠性和/或有效性的研究相对较少。此外，SLA 研究人员通常使用词汇多样性指数，例如 Root TTR（Guiraud 指数）和D（vocd-D 和 HD-D），这些指数已被初步证明在口语 L2 环境中缺乏可靠性和/或一直被证明缺乏可靠性。书面 L2 上下文中的可靠性。在本研究中，我们从可靠性（文本长度独立性和跨任务稳定性）的两个方面和有效性（与熟练程度分数的关系）的一方面来实证评估词汇多样性指数。结果表明，Root TTR 和D在不同的文本长度上都不可靠。然而，我们发现了对 MATTR 和 MTLD 优化版本的可靠性和有效性的支持。