Bibliographic coupling

Bibliographic coupling, like Co-citation, is a similarity measure that uses citation analysis to establish a similarity relationship between documents. Bibliographic coupling occurs when two works reference a common third work in their bibliographies. It is an indication that a probability exists that the two works treat a related subject matter.

Two documents are bibliographically coupled if they both cite one or more documents in common. The "coupling strength" of two given documents is higher the more citations to other documents they share. The figure to the right illustrates the concept of bibliographic coupling. In the figure, documents A and B both cite documents C, D and E. Thus, documents A and B have a bibliographic coupling strength of 3 - the number of elements in the intersection of their two reference lists.

Similarly, two authors are bibliographically coupled if the cumulative reference lists of their respective oeuvres each contain a reference to a common document, and their coupling strength also increases with the citations to other documents that their share. If the cumulative reference list of an author's oeuvre is determined as the multiset union of the documents that the author has co-authored, then the author bibliographic coupling strength of two authors (or more precisely, of their oeuvres) is defined as the size of the multiset intersection of their cumulative reference lists, however.

Bibliographic coupling can be useful in a wide variety of fields, since it helps researchers find related research done in the past. On the other hand, two documents are co-cited if they are both independently cited by one or more documents.

The concept of bibliographic coupling was introduced by M. M. Kessler of MIT in a paper published in 1963, and has been embraced in the work of the information scientist Eugene Garfield. It is one of the earliest citation analysis methods for document similarity computation and some have questioned its usefulness, pointing out that two works may reference completely unrelated subject matter in the third. Furthermore, bibliographic coupling is a retrospective similarity measure, meaning the information used to establish the similarity relationship between documents lies in the past and is static, i.e. bibliographic coupling strength cannot change over time, since outgoing citation counts are fixed.

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