The SpeechRater engine processes each response with an automated speech recognition system specially adapted for use with nonnative English. Based on the output of this system, natural language processing (NLP) and speech-processing algorithms are used to calculate a set of features that define a "profile" of the speech on a number of linguistic dimensions, including fluency, pronunciation, vocabulary usage, grammatical complexity and prosody. A model of speaking proficiency is then applied to these features in order to assign a final score to the response.
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