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From the Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minn. (Gami, Montori), the Department of Clinical Epidemiology and Biostatistics (Montori, Wilczynski, Haynes) and the Department of Medicine (Haynes), McMaster University, Hamilton, Ont.
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Abstract |
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Methods: We identified every article about diabetes mellitus in 170 hand-searched clinical journals published in 2000. For every article, we recorded the bibliographic citation and publication type (original or review article) and assessed the methodologic rigour. Citation information was obtained from the ISI Web of Knowledge in April 2003.
Results: Of 49 028 articles, 289 were about diabetes mellitus and had citation information. Citation counts ranged from 0 to 347 (median 6, interquartile range [IQR] 2–12). Author self-citation counts ranged from 0 to 16 (median 1, IQR 0–2). Author self-citations accounted for an average of 18% (95% confidence interval [CI] 15%–21%) and a median of 7% (95% CI 5%– 11%) of all citations of each publication that was cited at least once (n = 266). Original articles had double the mean proportion of author self-citations compared with review articles (19% v. 9%; median 7% v. 0%, difference 7%, 95% CI 0– 10%). Methodologic rigour and review type were not significantly associated with subsequent author self-citation.
Interpretation: Nearly one-fifth of all citations to articles about diabetes mellitus in clinical journals in the year 2000 were author self-citations. The frequency of self-citation was not associated with the quality of publications. These findings are likely applicable to the general clinical medicine literature and may have important implications for the assessment of journal or publication importance and the process of scientific discovery.
The scientific community uses bibliometric data, including citation counts of articles and impact factors of the journals in which the articles were published, to judge the importance of articles.3 Academic promotion committees similarly use these data to assess the productivity of faculty members and the scientific merit of their work.4 Author self-citations are not removed from citation counts or from the calculation of impact factors. As a result, author self-citations may misrepresent the importance of individual articles, skew the calculation of journal impact factors and bias perceptions of the importance of a publication.5 The effects of author self-citation on the process of research and discovery are unknown and potentially important.
Because the extent of author self-citation is unknown, we designed a study to identify the extent to which this practice occurs in the literature on diabetes mellitus, a major clinical field whose literature would represent the general medical literature, and to determine how self-citation relates to selected types of clinical articles and the quality of the reported research.
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Methods |
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On Apr. 1, 2003, the database contained 295 articles about diabetes therapy, prognosis, diagnosis, harm or cause. For each such publication, we retrieved the complete bibliographic citation, the article type and the methodologic grade. During the period Apr. 1–7, 2003, we queried the ISI Web of Knowledge (www.isiknowledge.com [a subscription is required]), which reports citation counts, impact factors and other bibliometric data. For 6 of the 295 articles, the ISI Web of Science did not track citations; these articles were excluded from further consideration. For each of the remaining 289 articles, we collected the citation count — the number of times the publication had been cited in subsequent publications. We examined every such citation, compared the lists of authors of the cited and citing publications, and identified the number of self-citations. Despite the large number of articles and citations, there was no instance in which article or author names caused confusion.
We created frequency tables of counts of author self-citations and all citations for the publications, categorized by type and methodologic rigour. Because the proportion of self-citations among all citations had a skewed distribution, we estimated the median. We also estimated the 95% confidence intervals (CIs) for the medians and for differences of medians (by study type and by methodologic rigour) using the bootstrapping technique with 10 000 iterations.
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Results |
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Original articles had double the mean proportion of author self-citations compared with review articles (19% v. 9%; median 7% v. 0%, difference 7%, 95% CI 0–10%). Methodologic rigour and review type were not significantly associated with subsequent author self-citation (Fig. 1).
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Interpretation |
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Author self-citation serves necessary functions in medical literature. It allows an author or group to expand on previous hypotheses, refer to established study designs and methods, and justify further investigations on the basis of prior results. Author self-citation may be inevitable when the published data in a specific field are solely the work of 1 investigator or research group. For example, we cited our own work once in this paper in order to refer the reader to relevant methodologic issues.
The greatest risk of author self-citation may be its effects on the process of scientific discovery. Citations build connectivity between publications, and this is essential to the growth and progression of medical knowledge.4 Repeated self-citation accentuates one's credibility or expertise7 and may perpetuate one's interpretations or opinions of specific research findings or general constructs. Self-citations, when pervasive, might falsely validate the conclusions of an author or group and could even limit scientific discovery if other investigators do not challenge what might be perceived as developing or accepted concepts.
To the extent that assessors of the importance of a publication rely on bibliometric indices based on citation counts (perhaps for lack of a better metric),4,5 author self-citation may artificially inflate an article's importance to the general scientific community. Author self-citation may even be performed knowingly for this purpose alone,7 a practice that has been satirized.8Apart from mere egotism, this practice may be promoted by the fact that citations are "a hallmark of academic achievement for authors and journals" and "correlate highly with the opinions of peers as to a scientist's contributions to his/her field and are used by medical school deans for promotion reviews." 4 One journal published an open call for authors to cite more recent articles from journals with a high impact factor to raise the former's impact factor.9 Although this would affect counts of journal self-citation (as opposed to author self-citation), it makes apparent the motivation and means by which citation counts may be manipulated. Our findings add to the debate regarding the role that bibliometric data should play in judgements about the scientific importance of published work.
ß See related article page 1929
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Footnotes |
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Contributors: Apoor Gami and Victor Montori conceived the study and acquired and analyzed the data. All of the authors were involved in study design and data interpretation. Victor Montori provided statistical expertise and study supervision. Apoor Gami drafted the manuscript. All of the authors provided critical revisions and approved the version to be published.
Acknowledgements: We thank other members of the research team, including Angela Eady, Susan Marks, Ann McKibbon, Doug Morgan, Cindy Walker-Dilks, Stephen Walter, Stephen Werre and Sharon Wong, for their contributions.
This study was funded by the US National Library of Medicine.
Competing interests: None declared.
Correspondence to: Dr. Apoor S. Gami, Division of Cardiovascular Diseases, Mayo Clinic, 200 First St. SW, Rochester MN 55905, USA; fax 507 255-7070; gami.apoor{at}mayo.edu
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