A citation index is a kind of bibliographic index, an index of citations between publications, allowing the user to easily establish which later documents cite which earlier documents. A form of citation index is first found in 12th-century Hebrew religious literature. Legal citation indexes are found in the 18th century and were made popular by citators such as Shepard's Citations (1873). In 1960, Eugene Garfield's Institute for Scientific Information (ISI) introduced the first citation index for papers published in academic journals, first the Science Citation Index (SCI), and later the Social Sciences Citation Index (SSCI) and the Arts and Humanities Citation Index (AHCI). The first automated citation indexing  was done by CiteSeer in 1997 and was patented. Other sources for such data include Google Scholar and Elsevier's Scopus.
The earliest known citation index is an index of biblical citations in rabbinic literature, the Mafteah ha-Derashot, attributed to Maimonides and probably dating to the 12th century. It is organized alphabetically by biblical phrase. Later biblical citation indexes are in the order of the canonical text. These citation indices were used both for general and for legal study. The Talmudic citation index En Mishpat (1714) even included a symbol to indicate whether a Talmudic decision had been overridden, just as in the 19th-century Shepard's Citations. Unlike modern scholarly citation indexes, only references to one work, the Bible, were indexed.
In English legal literature, volumes of judicial reports included lists of cases cited in that volume starting with Raymond's Reports (1743) and followed by Douglas's Reports (1783). Simon Greenleaf (1821) published an alphabetical list of cases with notes on later decisions affecting the precedential authority of the original decision.
The first true citation index dates to the 1860 publication of Labatt's Table of Cases...California..., followed in 1872 by Wait's Table of Cases...New York.... But the most important and best-known citation index came with the 1873 publication of Shepard's Citations.
Major citation indexing services
General-purpose, subscription-based academic citation indexes include:
- Web of Science by Clarivate Analytics (previously the Intellectual Property and Science business of Thomson Reuters)
- Scopus by Elsevier, available online only, which similarly combines subject searching with citation browsing and tracking in the sciences and social sciences.
Each of these offer an index of citations between publications and a mechanism to establish which documents cite which other documents. They are not open-access and differ widely in cost: Web of Science and Scopus are available by subscription (generally to libraries).
Several open-access, subject-specific citation indexing services also exist, such as:
- INSPIRE-HEP which covers high energy physics,
- PubMed, which covers life sciences and biomedical topics, and
- Astrophysics Data System which covers astronomy and physics.
Representativeness of proprietary databases
Clarivate Analytics' Web of Science (WoS) and Elsevier's Scopus databases are synonymous with data on international research, and considered as the two most trusted or authoritative sources of bibliometric data for peer-reviewed global research knowledge across disciplines. They are both also used widely for the purposes of researcher evaluation and promotion, institutional impact (for example the role of WoS in the UK Research Excellence Framework 2021[note 1]), and international league tables (Bibliographic data from Scopus represents more than 36% of assessment criteria in the THE rankings[note 2]). But while these databases are generally agreed to contain rigorously-assessed, high quality research, they do not represent the sum of current global research knowledge.
It is often mentioned in popular science articles that the research outputs of researchers in South America, Asia, and Africa is disappointingly low. Sub-Saharan Africa is often singled out and chastised for having "13.5% of the global population but less than 1% of global research output".[note 3] This oft-quoted fact is based on data from a World Bank/Elsevier report from 2012 which relies on data from Scopus.[note 4] Research outputs in this context refers to papers specifically published in peer-reviewed journals that are indexed in Scopus. Similarly, many others have analysed "global" or international collaborations and mobility using the even more selective WoS database. Research outputs in this context refers to papers specifically published in peer-reviewed journals that are indexed either in Scopus or WoS.
Both WoS and Scopus are considered highly selective. Both are commercial enterprises, whose standards and assessment criteria are mostly controlled by panels of gatekeepers in North America and Western Europe. The same is true for more comprehensive databases such as Ulrich's Web which lists as many as 70,000 journals, while Scopus has fewer than 50% of these, and WoS has fewer than 25%. While Scopus is larger and geographically broader than WoS, it still only covers a fraction of journal publishing outside North America and Europe. For example, it reports a coverage of over 2,000 journals in Asia ("230% more than the nearest competitor"),[note 5] which may seem impressive until you consider that in Indonesia alone there are more than 7,000 journals listed on the government's Garuda portal[note 6] (of which more than 1,300 are currently listed on DOAJ);[note 7] whilst at least 2,500 Japanese journals listed on the J-Stage platform.[note 8] Similarly, Scopus claims to have about 700 journals listed from Latin America, in comparison with SciELO's 1,285 active journal count;[note 9] but that's just the tip of the iceberg judging by the 1,300+ DOAJ-listed journals in Brazil alone.[note 10] Furthermore, the editorial boards of the journals contained in Wos and Scopus databases are integrated by researchers from western Europe and North America. For example, in the journal Human Geography, 41% of editorial board members are from the United States, and 37.8% from the UK. Similarly,) studied ten leading marketing journals in WoS and Scopus databases, and concluded that 85.3% of their editorial board members are based in the United States. It comes as no surprise that the research that gets published in these journals is the one that fits the editorial boards' world view.
Comparison with subject-specific indexes has further revealed the geographical and topic bias – for example Ciarli found that by comparing the coverage of rice research in CAB Abstracts (an agriculture and global health database) with WoS and Scopus, the latter "may strongly under-represent the scientific production by developing countries, and over-represent that by industrialised countries", and this is likely to apply to other fields of agriculture. This under-representation of applied research in Africa, Asia, and South America may have an additional negative effect on framing research strategies and policy development in these countries. The overpromotion of these databases diminishes the important role of "local" and "regional" journals for researchers who want to publish and read locally-relevant content. Some researchers deliberately bypass "high impact" journals when they want to publish locally useful or important research in favour of outlets that will reach their key audience quicker, and in other cases to be able to publish in their native language.
Furthermore, the odds are stacked against researchers for whom English is a foreign language. 95% of WoS journals are English consider the use of English language a hegemonic and unreflective linguistic practice. The consequences include that non-native speakers spend part of their budget on translation and correction and invest a significant amount of time and effort on subsequent corrections, making publishing in English a burden. A far-reaching consequence of the use of English as the lingua franca of science is in knowledge production, because its use benefits "worldviews, social, cultural, and political interests of the English-speaking center" ( p. 123).
The small proportion of research from South East Asia, Africa, and Latin America which makes it into WoS and Scopus journals is not attributable to a lack of effort or quality of research; but due to hidden and invisible epistemic and structural barriers (Chan 2019[note 11]). These are a reflection of "deeper historical and structural power that had positioned former colonial masters as the centers of knowledge production, while relegating former colonies to peripheral roles" (Chan 2018[note 12]). Many North American and European journals demonstrate conscious and unconscious bias against researchers from other parts of the world.[note 13] Many of these journals call themselves "international" but represent interests, authors, and even references only in their own languages.[note 14] Therefore, researchers in non-European or North American countries commonly get rejected because their research is said to be "not internationally significant" or only of "local interest" (the wrong "local"). This reflects the current concept of "international" as limited to a Euro/Anglophone-centric way of knowledge production. In other words, "the ongoing internationalisation has not meant academic interaction and exchange of knowledge, but the dominance of the leading Anglophone journals in which international debates occurs and gains recognition" (, p. 8).
Clarivate Analytics have made some positive steps to broaden the scope of WoS, integrating the SciELO citation index – a move not without criticism[note 15] – and through the creation of the Emerging Sources Index (ESI), which has allowed database access to many more international titles. However, there is still a lot of work to be done to recognise and amplify the growing body of research literature generated by those outside North America and Europe. The Royal Society have previously identified that "traditional metrics do not fully capture the dynamics of the emerging global science landscape", and that academia needs to develop more sophisticated data and impact measures to provide a richer understanding of the global scientific knowledge that is available to us.
Academia has not yet built digital infrastructures which are equal, comprehensive, multi-lingual and allows fair participation in knowledge creation. One way to bridge this gap is with discipline- and region-specific preprint repositories such as AfricArXiv and InarXiv. Open access advocates recommend to remain critical of those "global" research databases that have been built in Europe or Northern America and be wary of those who celebrate these products act as a representation of the global sum of human scholarly knowledge. Finally, let us also be aware of the geopolitical impact that such systematic discrimination has on knowledge production, and the inclusion and representation of marginalised research demographics within the global research landscape.
- Acknowledgment index
- Chinese Science Citation Database
- Citation analysis
- Emerging Sources Citation Index (ESCI)
- Google Scholar
- Index Copernicus
- Indian Citation Index
- Journal Citation Reports
- Korea Citation Index
- The Lens
- Microsoft Academic Search
- Russian Science Citation Index
- Scientific journal
- Semantic Scholar
- Serbian Citation Index
- "Clarivate Analytics will provide citation data during REF2021"..
- "World University Rankings 2019: Methodology"., Times Higher Education.
- "Africa produces just 1.1% of global scientific knowledge - but change is coming"..
- "A decade of development in sub-Saharan African science, technology, engineering, and Mathematics research" (PDF)..
- "Scopus content coverage guide" (PDF). Archived from the original (PDF) on 2019-09-04. Retrieved 2020-01-04., 2017.
- "Garuda portal"..
- "DOAJ journals from Indonesia"..
- "J-STAGE". portal.
- "SciELO". portal.
- "DOAJ journals from Brazil"..
- "Leslie Chan"., Twitter.
- "Open Access, the Global South and the Politics of Knowledge Production and Circulation"., Leslie Chan interview with Open Library of Humanities.
- "Richard Smith: Strong evidence of bias against research from low income countries"..
- "The Local and the Global: Puncturing the myth of the "international" journal"., Cameron Neylon.
- "SciELO, Open Infrastructure and Independence"., Leslie Chan.
- Giles, C. Lee, Kurt D. Bollacker, and Steve Lawrence. "CiteSeer: An automatic citation indexing system." In Proceedings of the third ACM conference on Digital libraries, pp. 89-98. 1998.
- SR Lawrence, KD Bollacker, CL Giles "Autonomous citation indexing and literature browsing using citation context; US Patent 6,738,780, 2004.
- Bella Hass Weinberg, "The Earliest Hebrew Citation Indexes" in Trudi Bellardo Hahn, Michael Keeble Buckland, eds., Historical Studies in Information Science, 1998, p. 51ff
- Bella Hass Weinberg, "Predecessors of Scientific Indexing Structures in the Domain of Religion" in W. Boyden Rayward, Mary Ellen Bowden, The History and Heritage of Scientific and Technological Information Systems, Proceedings of the 2002 Conference, 2004, p. 126ff
- Fred R. Shapiro, "Origins of Bibliometrics, Citation Indexing, and Citation Analysis: The Neglected Legal Literature" Journal of the American Society of Information Science 43:5:337-339 (1992)
- Mongeon, Philippe; Paul-Hus, Adèle (2016). "The Journal Coverage of Web of Science and Scopus: A Comparative Analysis". Scientometrics. 106: 213–228. arXiv:1511.08096. doi:10.1007/s11192-015-1765-5. S2CID 17753803.
- Archambault, Éric; Campbell, David; Gingras, Yves; Larivière, Vincent (2009). "Comparing Bibliometric Statistics Obtained from the Web of Science and Scopus". Journal of the American Society for Information Science and Technology. 60 (7): 1320–1326. arXiv:0903.5254. Bibcode:2009arXiv0903.5254A. doi:10.1002/asi.21062. S2CID 1168518.
- Falagas, Matthew E.; Pitsouni, Eleni I.; Malietzis, George A.; Pappas, Georgios (2008). "Comparison of PubMed, Scopus, Web of Science, and Google Scholar: Strengths and Weaknesses". The FASEB Journal. 22 (2): 338–342. doi:10.1096/fj.07-9492LSF. PMID 17884971.
- Alonso, S.; Cabrerizo, F.J.; Herrera-Viedma, E.; Herrera, F. (2009). "H-Index: A Review Focused in Its Variants, Computation and Standardization for Different Scientific Fields" (PDF). Journal of Informetrics. 3 (4): 273–289. doi:10.1016/j.joi.2009.04.001.
- Harzing, Anne-Wil; Alakangas, Satu (2016). "Google Scholar, Scopus and the Web of Science: A Longitudinal and Cross-Disciplinary Comparison". Scientometrics. 106 (2): 787–804. doi:10.1007/s11192-015-1798-9. S2CID 207236780.
- Robinson-Garcia, Nicolas; Chavarro, Diego Andrés; Molas-Gallart, Jordi; Ràfols, Ismael (2016-05-28). "On the Dominance of Quantitative Evaluation in 'Peripheral" Countries: Auditing Research with Technologies of Distance". SSRN 2818335.
- Vanholsbeeck, Marc; Thacker, Paul; Sattler, Susanne; Ross-Hellauer, Tony; Rivera-López, Bárbara S.; Rice, Curt; Nobes, Andy; Masuzzo, Paola; Martin, Ryan; Kramer, Bianca; Havemann, Johanna; Enkhbayar, Asura; Davila, Jacinto; Crick, Tom; Crane, Harry; Tennant, Jonathan P. (2019-03-11). "Ten Hot Topics around Scholarly Publishing". Publications. 7 (2): 34. doi:10.3390/publications7020034.
- Ribeiro, Leonardo Costa; Rapini, Márcia Siqueira; Silva, Leandro Alves; Albuquerque, Eduardo Motta (2018). "Growth Patterns of the Network of International Collaboration in Science". Scientometrics. 114: 159–179. doi:10.1007/s11192-017-2573-x. S2CID 19052437.
- Chinchilla-Rodríguez, Zaida; Miao, Lili; Murray, Dakota; Robinson-García, Nicolás; Costas, Rodrigo; Sugimoto, Cassidy R. (2018). "A Global Comparison of Scientific Mobility and Collaboration According to National Scientific Capacities". Frontiers in Research Metrics and Analytics. 3. doi:10.3389/frma.2018.00017.
- Boshoff, Nelius; Akanmu, Moses A. (2018). "Scopus or Web of Science for a Bibliometric Profile of Pharmacy Research at a Nigerian University?". South African Journal of Libraries and Information Science. 83 (2). doi:10.7553/83-2-1682.
- Wang, Yuandi; Hu, Ruifeng; Liu, Meijun (2017). "The Geotemporal Demographics of Academic Journals from 1950 to 2013 According to Ulrich's Database". Journal of Informetrics. 11 (3): 655–671. doi:10.1016/j.joi.2017.05.006. hdl:10722/247620.
- Gutiérrez, Javier; López-Nieva, Pedro (2001). "Are International Journals of Human Geography Really International?". Progress in Human Geography. 25: 53–69. doi:10.1191/030913201666823316. S2CID 144150221.
- Rosenstreich, Daniela; Wooliscroft, Ben (2006). "How International Are the Top Academic Journals? The Case of Marketing". European Business Review. 18 (6): 422–436. doi:10.1108/09555340610711067.
- "The Under-Representation of Developing Countries in the Main Bibliometric Databases: A Comparison of Rice Studies in the Web of Science, Scopus and CAB Abstracts". Context Counts: Pathways to Master Big and Little Data. Proceedings of the Science and Technology Indicators Conference 2014 Leiden. pp. 97–106.
- "Under-Reporting Research Relevant to Local Needs in the Global South. Database Biases in the Representation of Knowledge on Rice". Cite journal requires
- Chavarro, D.; Tang, P.; Rafols, I. (2014). "Interdisciplinarity and Research on Local Issues: Evidence from a Developing Country". Research Evaluation. 23 (3): 195–209. arXiv:1304.6742. doi:10.1093/reseval/rvu012. hdl:10251/85447. S2CID 1466718.
- Justice and the Dynamics of Research and Publication in Africa: Interrogating the Performance of "Publish or Perish". Uganda Martyrs University. 2017. ISBN 9789970090099.
- "The Reinterpretation of the Visibility and Quality of New Policies to Assess Scientific Publications". doi:10.17533/udea.rib.v40n3a04. Cite journal requires
- Paasi, Anssi (2015). "Academic Capitalism and the Geopolitics of Knowledge". The Wiley Blackwell Companion to Political Geography. pp. 507–523. doi:10.1002/9781118725771.ch37. ISBN 9781118725771.
- "The Victorious English Language: Hegemonic Practices in the Management Academy" (PDF). doi:10.1177/1056492612444316. S2CID 143610201. Cite journal requires
- Aalbers, Manuel B. (2004). "Creative Destruction through the Anglo-American Hegemony: A Non-Anglo-American View on Publications, Referees and Language". Area. 36 (3): 319–22. doi:10.1111/j.0004-0894.2004.00229.x.
- "The Inferior Science and the Dominant Use of English in Knowledge Production: A Case Study of Korean Science and Technology". doi:10.1177/1075547005275428. S2CID 144242790. Cite journal requires
- Rivera-López, Bárbara Sofía. "Uneven Writing Spaces in Academic Publishing: A Case Study on Internationalisation in the Disciplines of Biochemistry and Molecular Biology". doi:10.31237/osf.io/8cypr. Cite journal requires
- Lillis, Theresa M.; Curry, Mary Jane (2013). Academic writing in a global context: The politics and practices of publishing in English. ISBN 9780415468817.
- Minca, C. (2013). "(Im)Mobile Geographies". Geographica Helvetica. 68: 7–16. doi:10.5194/gh-68-7-2013.
- "Knowledge and Nations: Global Scientific Collaboration in the 21st Century". March 2011.
- Okune, Angela; Hillyer, Rebecca; Albornoz, Denisse; Posada, Alejandro; Chan, Leslie (2018). "Whose Infrastructure? Towards Inclusive and Collaborative Knowledge Infrastructures in Open Science". doi:10.4000/proceedings.elpub.2018.31. Cite journal requires