Referee for two papers by the same author: can I let them know?

Question

I am a referee for two papers by the same author: can I acknowledge in the second report (the first was almost ready when I was invited to referee the second one) my report to the first paper?

To give more details: I am suggesting acceptance to both papers, but I think the second one reexplains too much of what is developed in the first paper (with proper citation, but to a slightly different version in preprint), and I want to be able to tell the author they should simply cite the other work and move on to the new results. Furthermore, both papers make some odd choices about presentation, and it would be easier for me to simply point to the other report than to explain again in great detail why e.g. an alternative definition of some concept would make the work much easier to follow.

This is a single-blind peer review, so I know who the author is, but they don't know who I am. I don't see how doing this could be a problem (both in terms of ethics and etiquette), as they won't be able to tell who I am just from knowing I am a referee for both papers, but it seemed wiser to me to ask, rather than assume it is perfectly OK.

Edit: the papers were subjected to different journals, and are being handled by different editors. So it was just by coincidence that both ended up with me as a referee; but not a big coincidence because the field is rather small...

Edit 2: I have accepted Buffy's answer because of the general advice on how to proceed: contact the editors, and keep in mind that the first paper may not get accepted and that the author may get confused. But, in my specific case, I am following more or less quarague's suggestions: I am writing the two reports more or less independently, and referencing the preprint when talking about the first paper on the second report, but I will not make great efforts to hide that the two reports have been written by the same person (I will not explicitly mention it, but it will be clear from the similarities between the comments on both reports).

Answer 1

I suggest that you let the editor(s) know of your concerns before you put such things into the report itself. Take their advice.

Indicating you have seen the other paper might confuse the authors about the standards of the review process.

I've assumed this is for the same journal and likely the same editor. It is a little trickier if they are different journals. If the journals are different then you can ask both editors, assuming you are comfortable with that. Otherwise, I wouldn't include such things in either report. You can, of course, suggest changes.

Note that it is possible that one or the other of the papers won't be published, in spite of your recommendation.

Answer 2

My short advice would be to make the reviews independent, as far as feasible. While you say:

I don't see how doing this could be a problem (both in terms of ethics and etiquette)

I think this is an extremely unusual situation (as you yourself acknowledge). An author who recognizes the situation might feel that both papers' acceptances or rejections are riding in tandem on them getting both papers "right", especially if they are inexperienced.

While that stress is probably not too harmful, I can't see how it would be helpful or would result in better papers, so I would lean towards "first do no harm" in this situation and avoid unnecessarily stressing out the authors.

In terms of the situational specifics:

I want to be able to tell the author they should simply cite the other work and move on to the new results

Then you should just say that, based on the content of the preprint. If this issue arises in the final version of paper A but not the preprint, then as a reviewer I personally would just let it slide, since (1) under almost all circumstances these papers would be independently reviewed, and (2) it doesn't do significant harm to science to have two extremely closely written papers happen to repeat significant parts of each others' content.

both papers make some odd choices about presentation, and it would be easier for me to simply point to the other report

You could just cut and paste from one report to the other. If the presentations are a problem then they're a problem in each paper independent of the other paper's content -- so just comment on the problematic presentation as if that's the one paper you've read.

Answer 3

I see two issues you want to address here. First, the second paper rehashes a lot of what is already written in the first paper. As the first paper is available as a preprint and referenced in the second paper this issue is not related to you also reviewing the first paper. Your review for the second paper can simply critisize that aspect.

The other issue is that you want to suggest using slightly different definitions or naming conventions. This issue is present in both papers. I think the best solution here is to just copy a version of your argument into both reviews and adjust them as needed. That way each review can completely stand on its own but an astute reader would notice they are probably written by the same person. That is fine, there is no reason to hide that.