I don't know what it is but I know it when I hear it: Speaking proficiency and the ACTFL OPI

The Oral Proficiency Interview (OPI) that is used by the American Council on the Teaching of Foreign Languages (ACTFL) to assess speaking proficiency has become quite popular since its debut in the 1980s. As the OPI has been widely used for different purposes during the last thirty years, it has also been at the center of "...abundant and sustained professional engagement by foreign language teachers at all levels and in all languages, as well as intense and equally sustained criticism by specialists in foreign language testing" (Liskin-Gasparro, 2003, 483).;An impediment to research for language testers and a source of uncertainty for OPI users has been the lack of a clearly defined speaking proficiency construct underlying the OPI and its attendant rating procedure. This study identified, via automatic measurements of official OPI transcripts, seven aspects of examinee speech that significantly predicted holistic OPI ratings.;When entered into a step-wise regression, a single variable, examinees' number of word types divided by the square root of their word tokens, accounted for more than 85% of the variation in holistic OPI scores. When this single measure was used to provide retrodictive OPI ratings, they agreed with official ACTFL ratings 78% of the time, indicating that this measure of vocabulary breadth may be attended to by raters during the rating process. This paper concludes with an exploration of the predictor variables used to predict ratings, a discussion of the significance and limitations of this study, and suggestions for future research into the construct of the ACTFL OPI and Speaking Guidelines.