on evaluating web search with very few relevant documents
Many common web searches by their nature have a very small number of relevant documents. Homepage and "namedpage" searching are known-item searches where there is only a single relevant document. Topic distillation is a special kind of topical relevance search where the user wishes to find a few key web sites rather than every relevant web page. Because these types of searches are so common, web search evaluations have come to focus on tasks where there are very few relevant documents. Evaluations with few relevant documents pose special challenges for current metrics. In particular, the TREC 2003 topic distillation evaluation is unable to distinguish most submitted runs from each other.
evaluation web search search relevance documentation user web site web page types challenge metrication measurement error