Co-citation

[1] Like bibliographic coupling, co-citation is a semantic similarity measure for documents that makes use of citation analyses.

Documents co-cited at greater relative distances in the full text receive lower CPI values.

[6] Co-citation analysis provides a forward-looking assessment on document similarity in contrast to Bibliographic Coupling, which is retrospective.

[7] The citations a paper receives in the future depend on the evolution of an academic field, thus co-citation frequencies can still change.

[9] The motivations of authors for citing literature can vary greatly and occur for a variety of reasons aside from simply referring to academically relevant documents.

Documents A and B are cited by documents C, D and E, hence the documents A and B exhibit a co-citation strength of three. A more recent refinement of co-citation takes into account placement of citations with the document.
Figure visualizing co-citation on the left and a refinement of co-citation, Co-citation Proximity Analysis (CPA) on the right.