Exploiting Stopping Time to Evaluate Accumulated Relevance

Evaluation measures are more or less explicitly based on user models which abstract how users interact with a ranked result list and how they accumulate utility from it. However, traditional measures typically come with a hard-coded user model which can be, at best, parametrized. Moreover, they take a deterministic approach which leads to assign a precise score to a system run. In this paper, we take a different angle and, by relying on Markov chains and random walks, we propose a new family of evaluation measures which are able to accommodate for different and flexible user models, allow for simulating the interaction of different users, and turn the score into a random variable which more richly describes the performance of a system. We also show how the proposed framework allows for instantiating and better explaining some state-of-the-art measures, like AP, RBP, DCG, and ERR.