A study by Mario Malički, Ana Utrobičić and Ana Marušić, published in December in Biochemia Medica, provides insights into what journals do when duplicate publications are brought to their attention.
The authors tracked over five years the fate of more than a thousand of publications which were tagged as "duplicate publications" by the curated bibliographic database MEDLINE in January 2013. 35% of these turned out to be labelled incorrectly, and the rest constituted true cases of duplicate publications, amounting to the total of 359 cases. Most (56%) of these duplicates can be attributed to journals, usually publishing the same article in two issues of the journal; the rest can be attributed to authors, usually submitting the same study to several journals.
Tidying up of the duplications proved to be difficult: after checking the databases, journal pages, and several attempts at contacting editors, at the end of the study the authors found that only half of the cases were clearly labelled as duplications, and only 9% were retracted.
The Committee on Publication Ethics (COPE) recommends retraction of duplicated publications and provides a long list of case studies about the issue.
The corresponding author of the study, Mario Malički, was interviewed by Retraction Watch about the paper in January.