8. The method of claim 1 , 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.
1. A computer-implemented method, comprising: receiving a query and a current version of a document; receiving quality of result data for a plurality of versions of the document and the query, the quality of result data specifying a respective version-specific quality of result statistic for each of the versions of the document with respect to the query; calculating a weight for the version-specific quality of result statistics corresponding to each version of the document, wherein the weight for a particular version of the document is determined at least in part on an estimate of a difference between the particular version and the current version of the document, and wherein calculating the weight for a particular version of the document comprises: obtaining a representation of the particular version of the document, wherein the representation is a first time distribution of shingles, calculating a difference score by comparing the first time distribution of shingles representing the particular version of the document to a second time distribution of shingles representing the current version of the document, wherein each shingle is a contiguous subsequence of one or more tokens in the document, and wherein each shingle is associated with a particular time that the shingle is first observed in a version of the document such that a distribution of the times associated with the shingles in a version of the document corresponds to the representation of the version of the document, and using the difference score to calculate a corresponding weight for the particular version of the document; determining a weighted overall quality of result statistic for the document with respect to the query, wherein determining the weighted overall quality of result statistic comprises weighting each version-specific quality of result statistic with the calculated weight and combining the weighted version-specific quality of result statistics; and associating the weighted overall quality of result statistic with the document.