View source for Co-citation

{{Short description|Frequency with which two documents are cited together by other documents}}
[[File:Visualization of co-citation analysis methods.png|thumb|400px|right|alt=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.]]

'''Co-citation''' is the frequency with which two documents are ''cited'' together by other documents.<ref name="Small">{{Cite Q| Q56679837}}.</ref> If at least one other document cites two documents in common, these documents are said to be ''co-cited''. The more co-citations two documents receive, the higher their co-citation strength, and the more likely they are semantically related.<ref name="Small"/> Like [[Bibliographic coupling|bibliographic coupling]], co-citation is a [[Semantic similarity|semantic similarity]] measure for documents that makes use of [[Citation analysis|citation analyses]].

The figure to the right illustrates the concept of co-citation and a more recent variation of co-citation which accounts for the placement of citations in the full text of documents. The figure's left image shows the Documents A and B, which are both cited by Documents C, D and E; thus Documents A and B have a '''co-citation strength''', or '''co-citation index'''<ref name="Nicolaisen">Jeppe Nicolaisen, 2005 [http://www.iva.dk/bh/Core%20Concepts%20in%20LIS/articles%20a-z/cocitation_by_jeppe_nicolaisen.htm Co-citation] {{Webarchive|url=https://web.archive.org/web/20130315064318/http://www.iva.dk/bh/Core%20Concepts%20in%20LIS/articles%20a-z/cocitation_by_jeppe_nicolaisen.htm |date=2013-03-15 }}, in Birger Hjørland, ed., [http://www.db.dk/bh/Core%20Concepts%20in%20LIS/home.htm Core Concepts in Library and Information Science] {{webarchive|url=https://web.archive.org/web/20100525203337/http://www.db.dk/bh/core%20concepts%20in%20lis/home.htm |date=2010-05-25 }} from The Royal School of Library and Information Science (RSLIS), Copenhagen, Denmark.</ref> of three. This score is usually established using [[Citation index|citation index]]es. Documents featuring high numbers of co-citations are regarded as more similar.<ref name="Small"/>


The figure's right image shows a citing document which cites the Documents 1, 2 and 3. Both the Documents 1 and 2 and the Documents 2 and 3 have a co-citation strength of one, given that they are cited together by exactly one other document. However, Documents 2 and 3 are cited in much closer proximity to each other in the citing document compared to Document 1. To make co-citation a more meaningful measure in this case, a '''Co-Citation Proximity Index (CPI)''' can be introduced to account for the placement of citations relative to each other. Documents co-cited at greater relative distances in the full text receive lower CPI values.<ref name="Gipp">Bela Gipp and Joeran Beel, 2009 [http://gipp.com/wp-content/papercite-data/pdf/gipp09a.pdf "Citation Proximity Analysis (CPA) – A new approach for identifying related work based on Co-Citation Analysis"] in Birger Larsen and Jacqueline Leta, editors, Proceedings of the 12th International Conference on Scientometrics and Informetrics (ISSI’09), volume 2, pages 571–575, Rio de Janeiro (Brazil), July 2009.</ref> Gipp and Beel were the first to propose using modified co-citation weights based on proximity.<ref name="Boyack">Kevin W. Boyack, Henry Small and Richard Klavans, 2013 [http://sticonference.org/Proceedings/vol1/Boyack_Improving_155.pdf "Improving the Accuracy of Co-citation Clustering Using Full Text"] {{Webarchive|url=https://web.archive.org/web/20160304121440/http://sticonference.org/Proceedings/vol1/Boyack_Improving_155.pdf |date=2016-03-04 }} Journal of the American Society for Information Science and Technology, Volume 64, Issue 9, pages 1759–1767, September 2013</ref>

Henry Small<ref name="Small" /> and Irina Marshakova<ref>Irena Marshakova Shaikevich, 1973. [http://garfield.library.upenn.edu/marshakova/marshakovanauchtechn1973.pdf "System of Document Connections Based on References"]. Scientific and Technical Information Serial of VINITI, 6(2):3–8</ref> are credited for introducing co-citation analysis in 1973.<ref name="Nicolaisen"/> Both researchers came up with the measure independently, although Marshakova gained less credit, likely because her work was published in Russian.<ref>Frank Havemann, 2009. "Einführung in die Bibliometrie." Humboldt University of Berlin.</ref>

Co-citation analysis provides a forward-looking assessment on document similarity in contrast to Bibliographic Coupling, which is retrospective.<ref>Garfield, E., November 27, 2001. [http://garfield.library.upenn.edu/papers/drexelbelvergriffith92001.pdf "From Bibliographic Coupling to Co-Citation Analysis Via Algorithmic Historio-Bibliography: A Citationist’s Tribute to Belver C. Griffith.] a paper presented at the Drexel University, Philadelphia, PA.</ref> The citations a paper receives in the future depend on the evolution of an academic field, thus co-citation frequencies can still change. In the adjacent diagram, for example, Doc A and Doc B may still be co-cited by future documents, say Doc F and Doc G. This characteristic of co-citation allows for a dynamic [[Document classification|document classification]] system when compared to Bibliographic Coupling.

Over the decades, researchers proposed variants or enhancements to the original co-citation concept. Howard White introduced author co-citation analysis in 1981.<ref>Howard D. White and Belver C. Griffith, 1981. [http://onlinelibrary.wiley.com/doi/10.1002/asi.4630320302/abstract "Author Cocitation: A Literature Measure of Intellectual Structure."] Journal of the American Society for Information Science (JASIS), May, 1981 volume 32(3), pp. 163-171. -- the first ACA paper. DOI = 10.1002/asi.4630320302.</ref> Gipp and Beel proposed '''[[Co-citation Proximity Analysis]] (CPA)''' and introduced the CPI as an enhancement to the original co-citation concept in 2009.<ref name ="Gipp"/> Co-citation Proximity Analysis considers the proximity of citations within the full-texts for similarity computation and therefore allows for a more fine-grained assessment of semantic document similarity than pure co-citation.<ref>M. Schwarzer, M. Schubotz, N. Meuschke, C. Breitinger, [[Biography:Volker Markl|V. Markl]], and B. Gipp, [https://www.gipp.com/wp-content/papercite-data/pdf/schwarzer2016.pdf "Evaluating Link-based Recommendations for Wikipedia"] in Proceedings of the 16th ACM/IEEE-CS Joint Conference on Digital Libraries (JCDL), New York, NY, USA, 2016, pp. 191-200.</ref>

==Considerations==
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. Cole and Cole expressed this concern based on the observation that scientists tend to cite friends and research colleagues more frequently, a partiality known as ''cronyism''.<ref>Cole, J. R. & Cole, S., 1973. "Social Stratification in Science". Chicago, IL: University of Chicago Press.</ref> Additionally, it has been observed that academic works which have already gained much credit and reputation in a field tend to receive even more credit and thus citations in future literature, an observation termed the ''Matthew effect'' in science.

==See also==
* [http://www.isg.uni-konstanz.de/projects/citrec/ CITREC], an evaluation framework for citation-based similarity measures including [[Bibliographic coupling]], Co-citation, [[Co-citation Proximity Analysis]] and others.<ref name="Gipp2">Bela Gipp, Norman Meuschke & Mario Lipinski, 2015. [http://gipp.com/wp-content/papercite-data/pdf/gipp15b.pdf "CITREC: An Evaluation Framework for Citation-Based Similarity Measures based on TREC Genomics and PubMed Central"] in Proceedings of the iConference 2015, Newport Beach, California, 2015.</ref>

==References==
{{reflist}}

[[Category:Citation metrics]]

{{Sourceattribution|Co-citation}}