authorship - How to offer a reviewer to be co-author?

I currently have a paper submitted to PNAS. We had two rounds of revisions, and following detailed suggestions from one reviewer, we have improved our proposed algorithm a lot: its complexity is now significantly lower, and the idea he suggested makes the overall method more robust in handling noisy signal.

I feel that this reviewer's contribution extend far beyond his original role, so much that I feel it would be ethically honest to have him as a co-author. To be crystal-clear: if he was not a reviewer, but a colleague with whom I had discussed this before submitting the paper, he would clearly be entitled to authorship, no question.

But… he is a reviewer, so I am wondering how (if at all) we should ask him to join as co-author. Right now, I am ready to submit the twice-revised manuscript, and I have no doubt that it will be accepted (second review was “minor revisions”). The options I can see are:

• In my cover letter for the revised manuscript, explain the situation to the editor and ask him if he could (with the reviewer's agreement) lift anonymity and allow the authors' list change.


• Wait for the manuscript to be formally approved, and only then write to the editor asking for the same thing.


• Do nothing, for example because it is frowned upon. This would pain me greatly, because the reviewer really contributed very significantly to the algorithm, and I believe he should be able to claim authorship for this contribution (if he sees it fit).

So, what are accepted practices? How should I handle this matter?

Answer

Seconding other comments and answers: surely no one would be offended if you tried to make such an offer...

However, as already noted, if your offer is made prior to final acceptance, it might be misinterpreted, as your trying to clinch acceptance.

And that possibility surely has to be systematically excluded, so a foresightful editor and/or journal would surely not want to set such a precedent. A journal would not want authors to (be able to) solicit reviewers as co-authors, since this would create a conflict-of-interest situation, and cast doubt on the general validity and impartiality of their refereeing process!

That is, while it would be weird and awkward to publicly state such a policy, I would anticipate that the journal/editor would object as a matter of principle, to putting the reviewer on as a co-author.

Sensible reviewers would also understand this situation, for similar reasons, and in advance would expect no reward beyond "job well done". Even the anonymity of the referee should be maintained, as a matter of principle. Thus, we do often find effusive thanks to "the anonymous referee"...