Recent studies use user simulations to generate training corpora to learn dialog strategies automatically ( (Williams and Young, 2007), (Lemon and Liu, 2007)), or to evaluate dialog system performance (López-Cózar et al., 2003).
each student utterance was manually annotated for certainty (certain(cert), notcertain(ncert)) in a previous study based on both lexical and prosodic information 5 .