The effectiveness of combining information retrieval strategies for European languages

Building an effective Information Retrieval system requires various design choices, ranging from the weighting scheme to the type of morphological normalization. The combination of runs has become a standard technique to reap the benefits of dierent run types. Until now, systematic studies of the eectiveness of combination strategies have only been carried out for English. This paper provides an exploratory overview of the eectiveness of combination methods in nine European languages. We demonstrate that the combination of effective information retrieval strategies can lead to significant improvements of retrieval effectiveness. Furthermore, we analyze the relative impact of retrieving more relevant documents and of improved ranking of relevant documents. The experimental evidence is obtained using the 2003 testsuite of the cross-language evaluation forum (CLEF).