A unified model for metasearch and the efficient evaluation of retrieval systems via the hedge algorithm

We present a unified framework for simultaneously solving both the pooling problem (the construction of efficient document pools for the evaluation of retrieval systems) and metasearch (the fusion of ranked lists returned by retrieval systems in order to increase performance). The implementation is based on the Hedge algorithm for online learning, which has the advantage of convergence to bounded error rates approaching the performance of the best linear combination of the underlying systems. The choice of a loss function closely related to the average precision measure of system performance ensures that the judged document set performs well, both in constructing a metasearch list and as a pool for the accurate evaluation of retrieval systems. Our experimental results on TREC data demonstrate excellent performance in all measures---evaluation of systems, retrieval of relevant documents, and generation of metasearch lists.