Analysis of a new simulation approach to dialog system evaluation

The evaluation of spoken dialog systems still relies on subjective interaction experiments for quantifying interaction behavior and user-perceived quality. In this paper, we present a simulation approach replacing subjective tests in early system design and evaluation phases. The simulation is based on a model of the system, and a probabilistic model of user behavior. Probabilities for the next user action vary in dependence of system features and user characteristics, as defined by rules. This way, simulations can be conducted before data have been acquired. In order to evaluate the simulation approach, characteristics of simulated interactions are compared to interaction corpora obtained in subjective experiments. As was previously proposed in the literature, we compare interaction parameters for both corpora and calculate recall and precision of user utterances. The results are compared to those from a comparison of real user corpora. While the real corpora are not equal, they are more similar than the simulation is to the real data. However, the simulations can predict differences between system versions and user groups quite well on a relative level. In order to derive further requirements for the model, we conclude with a detailed analysis of utterances missing in the simulated corpus and consider the believability of entire dialogs. (C) 2009 Elsevier B.V. All rights reserved.