Evaluating ECAs - What,how and why?

One would like to rely on design guidelines for embodied conversational agents (ECAs), grounded on evaluation studies. How to define the physical and mental characteristics of an ECA, optimal for an envisioned application? What will be the added value of using an ECA? Although there have been studies addressing such issues, we are still far from getting a complete picture. This is not only due to the still relatively little experience with applications of ECAs, but also to the diversity in terms and experimental settings used. The lack of a common, established framework makes it difficult to compare ECAs, interpret evaluation results and judge their scope and relevance. In this paper we propose a common taxonomy of the relevant design and evaluation aspects of ECAs. We refer to recent works to elicit evaluation concepts and discuss measurement issues.