Predicting ESL learners’ oral proficiency by measuring the collocations in their spontaneous speech

Collocation, known as words that commonly co-occur, is a major category of formulaic language. There is now general consensus among language researchers that collocation is essential to effective language use in real-world communication situations (Ellis, 2008; Nesselhauf, 2005; Schmitt, 2010; Wray, 2002). Although a number of contemporary speech-processing theories assume the importance of formulaic language to spontaneous speaking (Bygate, 1987; de Bot, 1992; Kormos, 2006; Levelt, 1999), none of them gives an adequate explanation of the role that collocation plays in speech communication. In the practices of L2 speaking assessment, a test taker’s collocational performance is usually not separately scored mainly because human raters can only focus on a limited range of speech characteristics (Luoma, 2004). This paper argues for the centrality of collocation evaluation to communicationoriented L2 oral assessment. Based on a logical analysis of the conceptual connections among collocation, speech-processing theories, and rubrics for oral language assessment, I formulated a new construct called Spoken Collocational Competence (SCC). In light of Skehan’s (1998, 2009) trade-off hypothesis, I developed a series of measures for SCC, namely Operational Collocational Performance Measures (OCPMs), to cover three dimensions of learner collocation performance in spontaneous speaking: collocation accuracy, collocation complexity, and collocation fluency. I then investigated the empirical performance of these measures with 2344 lexical collocations extracted from sixty adult English as a second language (ESL) learners’ oral assessment data collected in two distinctive contexts of language use: conversing with an interlocutor on daily-life topics (or the SPEAK exam) and giving an academic lecture