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Avoiding plagiarism, self-plagiarism, and other questionable writing practices: A guide to ethical writing

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Salami Slicing (i.e., data fragmentation)

Guideline 11: Authors of complex studies should heed the advice previously put forth by Angell & Elman (1989): If the results of a single complex study are best presented as a ‘cohesive’ single whole, they should not be partitioned into individual papers. Furthermore, if there is any doubt as to whether a paper submitted for publication represents fragmented data, authors should enclose other papers (published or unpublished) that might be part of the paper under consideration.

Although often associated with redundant publication, the segmenting of a large study into two or more publications is somewhat different than reporting exactly the same data in two publications, but it is a similarly unacceptable scientific practice. As with redundant publication, salami slicing can lead to a distortion of the literature by leading unsuspecting readers to believe that data presented in each salami slice (i.e., journal article) is derived from a different subject sample. Consider the examples provided by Kassirer and Angell (1995), former editors of The New England Journal of Medicine:

“Several months ago, for example, we received a manuscript describing a controlled intervention in a birthing center. The authors sent the results on the mothers to us, and the results on the infants to another journal. The two outcomes would have more appropriately been reported together. We also received a manuscript on a molecular marker as a prognostic tool for a type of cancer; another journal was sent the results of a second marker from the same pathological specimens. Combining the two sets of data clearly would have added meaning to the findings.” (p. 450).

As with redundant and duplicate publication practices, this type of misrepresentation can distort the conclusions of literature reviews if the various segments of a salami publication that include data from a single subject sample are included in a meta analysis under the assumption that the data are derived from independent samples. For this reason, the breaking up of a complex study containing multiple dependent measures into separate smaller publications can have serious negative consequences for the integrity of the scientific database. In certain key areas of biomedical research the consequences can result in policy recommendations that could have adverse public health effects.

One element likely to be common to both redundant publication and salami publication is the potential for copyright infringement. This is because data or text (or both elements) appearing in one copyrighted publication will also appear in another publication whose copyright is owned by a different entity. Let’s turn our attention now to this topic.

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