There is no limitation to the number of co-authors on a paper. However, it is important to ensure that all of them have contributed in significant ways and can actually qualify to be a co-author. As per the ICMJE guidelines, authorship can be granted only to those who meet all of the following requirements:
- Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; AND
- Drafting the work or revising it critically for important intellectual content; AND
- Final approval of the version to be published; AND
- Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
In case come of the researchers do not meet all of the above criteria, they can be listed as contributors. For multi-author papers with a large number of authors, many journals prefer to have an authorship contribution statement listing the individual contributions of authors in the cover letter.
- How to draft the authorship contribution statement
- Authorship: An evolving concept
- Who can be included as a co-author of a paper?