9. The computer-readable memory device of claim 8 , where the one or more instructions to determine the frequency at which a document is selected further include: one or more instructions to determine the frequency at which the document is selected over time based on behavior of a single user.
8. A computer-readable memory device storing programming instructions that are executable by one or more processors of one or more devices, the programming instructions comprising: one or more instructions to determine a frequency at which a document is selected over time when the document is included in a set of search results, where the one or more instructions to determine the frequency at which the document is selected include: one or more instructions to determine a first rate at which the document is selected in a first time period, one or more instructions to determine a second rate at which the document is selected in a second time period, and one or more instructions to compare the first rate and the second rate to determine whether there is an increase or a decrease in the rate at which the document is selected between the first and second time periods; one or more instructions to generate a score for the document based on the frequency at which the document is selected over time when the document is included in a set of search results, where the one or more instructions to generate the score for the document include: one or more instructions to score the document based on whether there is an increase or a decrease in the rate at which the document is selected; and one or more instructions to rank the document with regard to at least one other document based on the score.