The freshness of Web search engine databases

This is a preprint of an article published in the Journal of Information Science Vol. 32, No. 2, 131-148 (2006). This study measures the frequency in which search engines update their indices. Therefore, 38 websites that are updated on a daily basis were analysed within a time-span of six weeks. The analysed search engines were Google, Yahoo and MSN. We find that Google performs best overall with the most pages updated on a daily basis, but only MSN is able to update all pages within a time-span of less than 20 days. Both other engines have outliers that are quite older. In terms of indexing patterns, we find different approaches at the different engines: While MSN shows clear update patterns, Google shows some outliers and the update process of the Yahoo index seems to be quite chaotic. Implications are that the quality of different search engine indices varies and not only one engine should be used when searching for current content