23. The storage device of claim 19 wherein the operations further comprise determining that a first past version of the first document during the first time period is different from a second past version of the first document during the second time period before modifying the first quality of result statistic.
23. The storage device of claim 19 wherein the operations further comprise determining that a first past version of the first document during the first time period is different from a second past version of the first document during the second time period before modifying the first quality of result statistic. 24. The storage device of claim 23 wherein determining that the first past version of the first document is different from the second past version of the first document comprises calculating a similarity score that is a measure of similarities between shingles extracted from the first past version of the first document and shingles extracted from the second past version of the first document, and determining that the similarity score satisfies a threshold.