The most common environment in which ranking is used takes a very specific form. Users sequentially generate queries in a digital library. For each query, ranking is applied to order a set of relevant items from which the user selects his favorite. This is the case when ranking search results for pages on the World Wide Web or for merchandize on an e-commerce site. In this work, we present a new online ranking algorithm, called NoRegret KLRank. Our algorithm is designed to use "clickthrough" information as it is provided by the users to improve future ranking decisions. More importantly, we show that its long term average performance will converge to the best rate achievable by any competing fixed ranking policy selected with the benefit of hindsight. We show how to ensure that this property continues to hold as new items are added to the set thus requiring a richer class of ranking policies. Finally, our empirical results show that, while in some context NoRegret KLRank might be considered conservative, a greedy variant of this algorithm actually outperforms many popular ranking algorithms.

Erick Delage @VideoLectures.net