5. The method of claim 2 , further comprising, for each set of documents, measuring a quality of the review of the documents in the set, the measure of quality of the review of each set being a function of at least one of: a number of documents for which the classifier model trained on that set outputs a different class from the class assigned based on the reviewer's label; and a number of documents for which at least one classifier model trained on another of the sets outputs a different class from the class assigned based on the reviewer's label.
2. The method of claim 1 , further comprising classifying the documents in a first of the sets of documents with a second classifier model trained on features of reviewed documents in a second of the sets of documents and their assigned classes.