16. The system of claim 15 , wherein the instructions further include instructions to: identify, for a second document of the search result documents, an additional set of one or more of the user attributes that are each associated with the second document; identify, for each of the user attributes of the additional set, a second document bias measure for the second document; determine a second document overall bias measure for the second document based on the second document bias measures for the user attributes of the additional set; and determine a ranking of the second document based on the second document overall bias measure.
16. The system of claim 15 , wherein the instructions further include instructions to: identify, for a second document of the search result documents, an additional set of one or more of the user attributes that are each associated with the second document; identify, for each of the user attributes of the additional set, a second document bias measure for the second document; determine a second document overall bias measure for the second document based on the second document bias measures for the user attributes of the additional set; and determine a ranking of the second document based on the second document overall bias measure. 17. The system of claim 16 , wherein one or more of the user attributes of the set are not present in the additional set.