34. The computer-readable medium of claim 27 , further comprising: associating the document with a non-weighted overall quality of result statistic; receiving the query, and in response to receiving the query, determining whether to select either the weighted overall quality of result statistic or the non-weighted overall quality of result statistic; selecting either the weighted overall quality of result statistic or the non-weighted overall quality of result statistic in response to the determination; and providing the selected overall quality of result statistic to a ranking engine implemented on one or more computers.
34. The computer-readable medium of claim 27 , further comprising: associating the document with a non-weighted overall quality of result statistic; receiving the query, and in response to receiving the query, determining whether to select either the weighted overall quality of result statistic or the non-weighted overall quality of result statistic; selecting either the weighted overall quality of result statistic or the non-weighted overall quality of result statistic in response to the determination; and providing the selected overall quality of result statistic to a ranking engine implemented on one or more computers. 35. The computer-readable medium of claim 34 , further comprising determining a difference score for the reference version of the document and a current version of the document, and wherein selecting either the weighted overall quality of result statistic or non-weighted overall quality of result statistic comprises selecting a statistic according to the difference score.