1. A method of reviewing documents comprising: partitioning a collection of documents into sets of documents for review by a plurality of reviewers; for each set: organizing the documents in the set into a plurality of groups, displaying documents in the set on a display device for review by a reviewer, receiving the reviewer's labels for the displayed documents, based on the reviewer's labels, assigning a class from a plurality of classes to each of the reviewed documents, progressively training a classifier model stored in computer memory based on features extracted from the reviewed documents in the set and their assigned classes; and prior to review of all documents in the set, identifying documents in the set for which the classifier model assigns a class different from the one assigned based on the reviewer's label and returning a subset of the identified documents for a second review by a reviewer.