Identifying linguistic correlates of speaking ability is an important domain of research in second language (L2) speaking assessment, which contributes to the understanding of speaking ability as a theoretical construct.
The standard practice of linguistic analysis in validation research starts with quantifying an array of linguistic features of test performances, followed by dimension reduction techniques to identify underlying dimensions of speaking ability. However, existing research varies considerably in the selection of linguistic features, falling largely under one of three approaches, namely, (1) the CAF-based approach which operationalises speaking ability through form-focused features; (2) the register-linguistic approach which explores lexico-grammatical features in relation to linguistic functions; and (3) acoustic-pronunciation features related to speech intelligibility and comprehensibility.
While there is a large body of literature in each strand, fewer studies have combined features from all three strands.
The present study examined a wide range of linguistic features selected from all three approaches on 280 benchmark performances from Band 5 to 8 on the IELTS speaking test, to identify meaningful linguistic correlates of IELTS speaking ability.
Descriptive statistics and correlational analyses revealed a number of linguistic features in each category that correlate significantly with IELTS band scores. Findings of this study reflect the different subconstructs of speaking ability and provide validity evidence for the IELTS speaking test.