ORIGINAL CONTRIBUTION Different Patterns of Duplicate Publication An Analysis of Articles Used in Systematic Reviews Erik von Elm, MD Greta Poglia Bernhard Walder, MD Martin R. Trame `r, MD, DPhil D UPLICATE PUBLICATION IS THE publication of an article that overlaps substantially with an article published else- where. 1 This practice may be accept- able in particular situations. However, authors must acknowledge the main ar- ticle overtly by using a cross-reference. Covert duplicate publication has been widely disapproved. 2,3 This practice is wasteful of the time and resources of edi- tors, peer reviewers, and readers, and it is misleading because undue weight is given to observations that are being re- ported repeatedly. When duplicates are inadvertently included in a systematic review, the conclusion of that system- atic review may change. 4 Finally, co- vert duplicate publication is dishonest; it undermines the integrity of science. 5 Little is known about patterns of duplicate publication. Also, character- istics of duplicates are not well under- stood, and there is no common agree- ment on how to classify them. We set out to investigate patterns of dupli- cate publication and to propose a de- cision tree for their classification. We have chosen systematic reviews as a source of information because dupli- cates are often identified during the rig- orous process of a systematic review. 6 METHODS Identification of Duplicates We used a comprehensive list of sys- tematic reviews (1989 through Au- gust 15, 2002) in perioperative medi- cine (anesthesia, analgesia, and critical care) that is regularly updated through searches in electronic databases, hand- searching of specialty journals, and con- tact with experts. 7 The average meth- odological quality of these reviews was considered satisfactory. 8 We selected all systematic reviews of anesthesia and analgesia topics that ac- Author Affiliations: Division of Anesthesiology, De- partment of Anesthesiology, Pharmacology, and Sur- gical Intensive Care, Geneva University Hospitals, Geneva, Switzerland. Dr von Elm is now with the De- partment of Social and Preventive Medicine, Univer- sity of Bern, Bern, Switzerland; and Mrs Poglia is now with the Department of Psychiatry, Geneva Univer- sity Hospitals, Geneva, Switzerland. Corresponding Author: Martin R. Trame ` r, MD, DPhil, Division of Anesthesiology, Geneva University Hos- pitals, CH-1211 Geneva 14, Switzerland (martin .tramer@hcuge.ch). Context Duplicate publication is publication of an article that overlaps substantially with an article published elsewhere. Patterns of duplication are not well understood. Objective To investigate duplication patterns and propose a decision tree for clas- sification. Data Sources We searched a comprehensive list of systematic reviews (1989 through August 15, 2002) in anesthesia and analgesia that is accessible on the Internet. We selected published full articles of duplicates that had been identified in these system- atic reviews. Abstracts, letters, or book chapters were excluded. Study Selection and Data Extraction Authors of 56 (40%) of 141 systematic reviews acknowledged identification of duplicates. Duplication patterns were identi- fied independently by all investigators comparing samples and outcomes of pairs of duplicates and main articles. Information on cross-reference, sponsorship, authorship, and publication characteristics was extracted from the articles. Data Synthesis The 56 systematic reviews included 1131 main articles (129 337 sub- jects) and excluded 103 duplicates (12 589 subjects) that originated from 78 main ar- ticles. Sixty articles were published twice, 13 three times, 3 four times, and 2 five times. We identified 6 duplication patterns: (1A) identical samples and identical outcomes (21 pairs); (1B) same as 1A but several duplicates assembled (n = 16); (2) identical samples and different outcomes (n = 24); (3A) increasing sample and identical outcomes (n = 11); (3B) decreasing sample and identical outcomes (n = 11); (4) different samples and differ- ent outcomes (n = 20). The prevalence of covert duplicate articles (without a cross- reference to the main article) was 5.3% (65/1234). Of the duplicates, 34 (33%) were sponsored by the pharmaceutical industry, and 66 (64%) had authorship that differed partly or completely from the main article. The median journal impact factor was 1.8 (range, 0.1-29.5) for duplicates and 2.0 (range, 0.4-29.5) for main articles (P = .13). The median annual citation rate was 1.7 (range, 0-27) for duplicates and 2.1 (range, 0-31) for main articles (P = .45). The median number of authors was 4 (range, 1-14) for duplicates and 4 (range, 1-15) for corresponding main articles (P = .02). The median delay in publication between main articles and duplicates was 1 year (range, 0-7 years). Conclusions Duplication goes beyond simple copying. Six distinct duplication pat- terns were identified after comparing study samples and outcomes of duplicates and corresponding main articles. Authorship was an unreliable criterion. Duplicates were published in journals with similar impact factors and were cited as frequently as main articles. JAMA. 2004;291:974-980 www.jama.com 974 JAMA, February 25, 2004—Vol 291, No. 8 (Reprinted) ©2004 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 05/26/2020