Abstract: A method of ranking documents by specificity values includes specifying a reference set of documents, each document including one or more terms, and specifying a first document that includes one or more terms that are included in the reference set of documents. The method includes determining, from the reference set of documents, one or more term-specificity values for the one or more terms of the first document by calculating frequencies of terms within the reference set of documents, wherein a larger term-specificity value corresponds to a lower likelihood relative to the reference set of documents, and determining a document-specificity value for the first document by combining the one or more term-specificity values for the first document, wherein larger term-specificity values correspond to a larger document-specificity value.