Context Duplicate publication is publication of an article that overlaps substantially
with an article published elsewhere. Patterns of duplication are not well
Objective To investigate duplication patterns and propose a decision tree for
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 systematic 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 identified 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
subjects) and excluded 103 duplicates (12 589 subjects) that originated
from 78 main articles. 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 different
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 patterns
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.