Two closely related journals received a series of manuscripts each based on descriptions of a complex medical procedure by multicentre consortia. At least three separate consortia submitted three separate papers. Each consortium included centres which were shared between the three groups and likely have the same patients/procedures represented in different reports.
For example:
Consortium 1 includes patients from hospital A, B, C
Consortium 2 includes patients from hospital B, D, E
Consortium 3 includes patients from hospital B, E, F, G
(note that hospital B's patients appear in all three studies).
While there were slight variations in the manuscripts, they each described the same procedure, eg, one paper described procedure A outcomes versus procedure B; procedure A outcomes versus procedure C; a third manuscript compared procedure B outcomes versus procedure C.
One of the journals is concerned that patients are being represented more than once, and thus future analyses, and meta-analyses, which assume unique patients, will over count the value of each study. On the other hand, they want to encourage multicentre collaboration, especially on new and emerging procedures.
Questions for COPE Council
- Should patients included in one consortium be excluded from another consortium or is it sufficient to just report the number of overlapping patients (eg, this study includes patients who have previously been reported in ....[reference]).
- When does slight variations of themes (comparing procedure A to B, and then comparing procedure A to C) represent unethical duplication?
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.
This would appear to be an example of salami-slicing. There seems to be one procedure and one body of people, spread across five collaborating institutions. The multicentre collaboration should have submitted a single manuscript reporting on all findings at the same time. Anything else is duplication. Patients should not be included more than once in study results and journals should not accept outcome splitting. If one umbrella consortium could be created from the three, and the papers condensed into one, that would be the ideal outcome.
The editor might consider checking the original study protocol. Has the study been registered?
The concerns about multiple overlapping papers vitiating potential use of the data for future meta-analyses are also well founded.
The editors are to be congratulated for acting responsibly in this matter despite the wishes of the authors. Their actions have been in the interests of patients and the scientific community.