Every month, more than 130 billion queries worldwide are entered into the search boxes of general-purpose web search engines (ComScore, 2010). This enormous number shows that web searching is not only a large business, but also that many people rely on the search engines' results when researching information. A goal of all search engine evaluation efforts is to generate better systems. This goal is of major importance to the search engine vendors who can directly apply evaluation results to develop better ranking algorithms.