Web impact factors and search engine coverage

This is an accepted manuscript of an article published by MCB UP Ltd in Journal of Documentation on 01/04/2000, available online: https://doi.org/10.1108/00220410010803801 The accepted version of the publication may differ from the final published version.Search engines index only a proportion of the web and this proportion is not determined randomly but by following algorithms that take into account the properties that impact factors measure. A survey was conducted in order to test the coverage of search engines and to decide whether their partial coverage is indeed an obstacle to using them to calculate web impact factors. The results indicate that search engine coverage, even of large national domains is extremely uneven and would be likely to lead to misleading calculations