1. A method comprising: receiving, by a processing device, data representing a plurality of corpora, each of the plurality of corpora including a set of documents; receiving, by a processing device, data representing terms that appear in the corpora; for each one of the terms, determining, by a processing device, a plurality of inverse document frequency values each associated with a respective one of the plurality of corpora; receiving, by a processing device, data representing a subset of the terms that also appear in a document; for each term in the subset of the terms, determining, by a processing device, a term frequency for the term in the document; and for each term in the subset of the terms, determining, by a processing device, an augmented term frequency-inverse document frequency value based on: (i) the term frequency, and (ii) the plurality of inverse document frequency values that were determined for the term in the subset of the terms.