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Models and metrics: IR evaluation as a user process

Retrieval system effectiveness can be measured in two quite different ways: by monitoring the behavior of users and gathering data about the ease and accuracy with which they accomplish certain specified information-seeking tasks; or by using numeric effectiveness metrics to score system runs in reference to a set of relevance judgments. The former has the benefit of directly assessing the actual goal of the system, namely the user's ability to complete a search task; whereas the latter approach has the benefit of being quantitative and repeatable. Each given effectiveness metric is an attempt to bridge the gap between these two evaluation approaches, since the implicit belief supporting the use of any particular metric is that user task performance should be correlated with the numeric score provided by the metric. In this work we explore that linkage, considering a range of effectiveness metrics, and the user search behavior that each of them implies. We then examine more complex user models, as a guide to the development of new effectiveness metrics. We conclude by summarizing an experiment that we believe will help establish the strength of the linkage between models and metrics.