Author order - seniority vs contribution

Question

I have a manuscript (in the field of biomedical research) close to submission with four authors: me (as first author) (ME), my ex-boss (as senior author) (EB) and two more authors of which one is a very senior professor (SP) and the other one is a junior professor (JP).

The SP contributed considerably more than the JP. My question is now which order of the authors would be more appropriate:

1. ME, SP, JP, EB (higher contribution of SP means further to the front)
2. ME, JP, SP, EB (SP is more senior therefore closer to the senior author position (which is already occupied by EB) and it is not going to be a shared senior authorship)

I will of course ask them directly but I would like go get some opinions first ...

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All authors are professors and independent PIs without a hierarchy between them.

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We discussed it and decided for the option:

ME, SP, JP, EB

Answer 1

I'm not in your field, but personally I would lean towards option #1

1. You, SP, JP, EB (higher contribution of SP means further to the front)

since that seems to be the appropriate order given the relative contributions (neglecting other concerns). Since all authors (including JP) are professors, the distinction between second and third author shouldn't matter much at all. Of course, individual concerns might exist. For example, JP could potentially benefit more from having an additional near-senior author paper in future evaluations, see answers to this question. Or SP might prefer the near-senior position.

In your situation I'd propose option #1 (possibly by sending out a draft of the paper), and asking if it looks good to them, or if they want to change the order.

Answer 2

Assuming you are a junior researcher like a PhD student, I would defer to the professors to sort this issue out themselves. Voicing any opinions about this matter could have a non-zero probability of stepping on someone's toes.

Given that, there is essentially no perceived difference between second and third author. And in the two possibilities you just described, all authors 'get their due', so there is no issue about fairness here either.