This is a hypothetical situation based on a real-life experience.
A set of authors recruited the same patient cohort, collected data with two questionnaires, took one blood sample, but tests were done by two research students for two pathogens, and the results were presented separately in two theses. Subsequently, they sent different papers to two journals. No plagiarism has been identified between the papers.
The Editor of one journal is a reviewer for the other and they picked up the similarities based on the study sites, inclusion criteria, etc that indicate this is the same patient cohort, and the same sample has been tested for two organisms. We are concerned that this could be a case of salami slicing.
Question:
- What is the recommendation in this situation?
Advice on this case is from a small number of COPE Council Members. Most cases on the COPE website are presented to the COPE Forum where advice is offered by a wider group of COPE Members and COPE Council Members. Advice on individual cases is not formal COPE guidance.
There should be a strong rationale for reporting a study of one cohort in separate publications and a subject expert should decide whether it is warranted in any given case. Simply having two students each of whom needs a publication is not a strong rationale. The first journal should have been fully informed and given the choice of how to handle the reporting of the two sub-studies. If the first article has not been published yet, the two editors could discuss if the first article could still be revised and re-reviewed. If the first article has been published, the second article needs to cite it and explain that the cohort is the same and what has been already previously reported, so as not to distort future meta-analyses. Even if there may be no overlap in control samples or repetition of questionnaire data, the second article should still cite the first article and explain that the cohort and origin of the tissue sample is the same.
However, it would be permissible to publish two studies on the same cohort if they asked very different questions. In some fields this may be quite common, for example, if samples are hard to fabricate; in others, there is a greater risk of unethical ‘salami slicing’, duplication, or redundancy because of pressures on students and junior researchers to publish. Again, this is a judgement that should be made by a subject expert who will want to bear in mind factors such as whether the papers are split only by outcome, inclusion criteria (for example, based on the same study question but focusing on different sub-groups of participants), or methodology. An additional consideration could be whether the data for both studies were available at the time of the first submission.
To summarise, multiple publications from the same cohort would be considered unethical if:
1. The study questions are closely related, and the judgment of the Editor/expert in the field is that the authors could have easily incorporated both papers into one more substantial publication.
2. The authors were not transparent about the fact that another "related" study was submitted elsewhere. Submission of two or more related papers should be justified.
The editors may also find the COPE case on Salami slicing useful.
Further resources
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COPE Flowchart on Handling redundant (duplicate) publication in a submitted manuscript
- COPE Flowchart on Handling redundant (duplicate) publication in a published article