Co‐citation in the scientific literature: A new measure of the relationship between two documents

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We can also give a more formal definition of co‐citation in terms of set theory notation. If A is the set of papers which cites document a and B is the set which cites b then A∩B is the set which cites both a and b. The number of elements in A∩B that is n(A∩B) is the co‐citation frequency. The relative co‐citation frequency could be defined as n(A∩B) ÷ n(A∪B).

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Programs are currently being developed for automatically determining co‐citation and using these data as input to a cluster generating program. The results of some preliminary experiments using this system to examine scientific specialties will be reported in a forthcoming paper.