The effectiveness of combining information retrieval strategies for European languages

Building an e#ective 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 di#erent run types. Until now, systematic studies of the e#ectiveness of combination strategies have only been carried out for English. This paper provides an exploratory overview of the e#ectiveness of combination methods in nine European languages. We demonstrate that the combination of e#ective information retrieval strategies can lead to significant improvements of retrieval e#ectiveness. 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).