13. The system of claim 8 , where at least one of the one or more server devices is further to: compare the respective first scores to a threshold value; and remove one of the search results, that has a respective first score that is less than the threshold value, before generating the second scores for the categories, where the second scores are generated without using information regarding the removed one of the search results.
8. A system, comprising: one or more server devices to: receive a search query from a client device; identify documents as search results relevant to the search query, where each of the search results has a respective first score; rank the search results, based on the respective first scores, to form a ranked list of search results, where each of the search results has a respective position, within the ranked list, that is based on the ranking; determine a selection rate corresponding to each of the positions in the ranked list, a particular selection rate, corresponding to a particular position, being determined based on selections from the particular position, and the one or more devices, when determining the selection rate for one of the positions in the ranked list, being further to: selectively: obtain information regarding an actual selection rate, corresponding to the one of the positions, from observed selections, or estimate a selection rate corresponding to the one of the positions, and use the actual selection rate or the estimated selection rate as the selection rate for the one of the positions; identify categories with which the search results are associated; generate second scores for the categories based on the selection rates, where the second score, for a particular one of the categories, is based on the selection rate corresponding to the position, in the ranked list, of one or more of the search results that are associated with the particular one of the categories, the one or more server devices generating the second score, for one of the categories, based on a combination of a plurality of selection rates corresponding to positions, in the ranked list, of a set of the search results that are associated with the one of the categories; select a plurality of the categories based on the second scores of the categories; select a plurality of the search results for the selected plurality of categories; generate a search result document that includes information regarding the selected plurality of categories and information regarding the selected plurality of search results; and provide the search result document for display on the client device.