Previous scalability experiments found that early precision improves as collection size increases. However, that was under the assumption that a collection's documents are all sampled with uniform probability from the same population. We contrast this to a large breadth-first web crawl, an important scenario in real-world Web search, where the early documents have quite different characteristics from the later documents. Having observed that NDCG@100 (measured over a set of reference queries) begins to plateau in the initial stages of the crawl, we investigate a number of possible reasons for this behaviour. These include the web-pages themselves, the metric used to measure retrieval effectiveness as well as the set of relevance judgements used.

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In  Proceedings of the 31st European Conference on Information Retrieval (ECIR)

Publisher  Springer Verlag
All copyrights reserved by Springer 2007.

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