Swapping documents and terms

Experiments were conducted to explore the impact of combining various components of eight leading information retrieval systems. Each system demonstrated improved effectiveness through the use of blind feedback, also known as pseudo-relevance feedback, a form of query expansion. Blind feedback uses the results of a preliminary retrieval step to augment the efficacy of a secondary retrieval step. The hybrid combination of primary and secondary retrieval steps from different systems in a number of cases yielded better effectiveness than either of the constituent systems alone. This positive combining effect was observed when entire documents were passed between the two retrieval steps, but not when only the expansion terms were passed. Several combinations of primary and secondary retrieval steps were fused using the CombMNZ algorithm; all yielded significant effectiveness improvement over the individual systems, with the best yielding an improvement of 13% (p = 10⁻⁶) over the best individual system and an improvement of 4% (p = 10⁻⁵) over a simple fusion of the eight systems.