18. The system of claim 14 , wherein determining the weighted overall quality of result statistic comprises: determining a respective difference score for each of the plurality of versions of the document with reference to the reference version of the document, wherein the difference score for a particular version in the plurality of versions of the document and the reference version of the document measures a difference between a representation of the particular version and a representation of the reference version of the document; and weighting each version-specific quality of result statistic by a weight derived from the difference score for the version of the document associated with the version-specific quality of result statistic.
18. The system of claim 14 , wherein determining the weighted overall quality of result statistic comprises: determining a respective difference score for each of the plurality of versions of the document with reference to the reference version of the document, wherein the difference score for a particular version in the plurality of versions of the document and the reference version of the document measures a difference between a representation of the particular version and a representation of the reference version of the document; and weighting each version-specific quality of result statistic by a weight derived from the difference score for the version of the document associated with the version-specific quality of result statistic. 20. The system of claim 18 , wherein the representation of a version of the document comprises a time distribution of shingles in the version of the document.