The fraction of all Documents that two reviewers code the same way. While high Agreement is commonly advanced as evidence of an effective review effort, its use can be misleading, for the same reason that the use of Accuracy can be misleading. When the vast majority of Documents in a Population are Not Relevant, a high level of Agreement will be achieved when the reviewers agree that these Documents are Not Relevant, irrespective of whether or not they agree that any of the Relevant Documents are Relevant.