Research on second language acquisition has used various quantitative and qualitative measures to assess oral proficiency, yet there is little empirical research comparing these measures. Comparisons between quantitative measures and native speaker ratings are especially rare. Four of the most common quantitative measurements applied in L2 research include the type-token ratio as a measure of lexical diversity; the T-unit as a measure of syntactic complexity; the error-free t-unit as a measure of grammatical accuracy; and average speech rate as a measure of fluency. The present study compares these four quantitative measures of oral proficiency and one qualitative measure of oral proficiency, i.e., native speaker ratings, based on the speech of three non-native English speakers during the International English Language Testing System (IELTS) oral interview. The results indicate that measures of syntactic complexity and speed fluency correlate with native speaker ratings; however, the measure of lexical diversity does not correlate with the native speaker ratings. Interestingly, the measure of grammatical accuracy displays an inverse relationship to the native speaker ratings. These results are discussed in light of an accuracy-fluency continuum. This finding demonstrates the importance of careful consideration in determining which measure of oral proficiency is appropriate for a given research context.
Christoffersen, K. O. (2017). Comparing native speaker ratings and quantitative measures of oral proficiency in IELTS interviews. Elia, (17), 233-250. http://dx.doi.org/10.12795/elia.2017.i17.10
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