11. The computer program product of claim 8 , wherein the operations further comprise combining additional click data with the combined weighted click data to generate the score, wherein the additional click data indicates how frequently the document was selected when the document was presented in search results for the search query.
12. The computer program product of claim 11 , wherein the combined weighted click data is adjusted by a blending factor before it is combined with the additional click data, wherein the blending factor indicates a degree to which the click data for the document and the one or more related search queries reliably indicates user behavior with regard to the search query.