Would it be ethical for students working on the same team to include in their Ph.D. theses results arising from joint publications, ending up in different dissertations containing almost identical chapters?

Of course, the students should at least mention that the common chapters are excerpted from a joint publication. However, wouldn't a significant overlap at least indicate that the students have been unable to come up with enough strong and coherent results to make their own independent dissertations?

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    Hi user4423, and welcome. We're looking for a single question with an objective answer. Which of your two distinct questions would you like us to answer? The one starting "Would it be ethical ... " (likely to be closed as not constructive) or the one starting "wouldn't a significant overlap indicate ..." (to which "It depends. Not necessarily" is the meaningful and correct answer)? – 410 gone Dec 23 '12 at 17:43
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    Hi, thanks for the feedback. Sorry for the confusion: There is actually just one question, which is the one given in the title. The two subquestions are intended to give more details about the general issue of whether it is considered appropriate to publish the very same results in two different theses. I found the answers received so far to be quite useful. – user4423 Dec 23 '12 at 22:31

I think for a PhD thesis it is important the writer has enough original and new contributions to earn the PhD degree. When two PhD's work closely together, and write joint publications this can only work if it is clear that both PhD's have made new and significant contributions.

For example, in a publication which has both lab experiments and numerical modeling it is easy to see that both the lab-PhD and the numerical-PhD have done different things, which are put together jointly into a publication. In this case I would think it ethical that both PhD's get their degree based on the same publications. If, however, the overlap is not countered by the fact that the PhD's each have their distinct niche, I would not find it ethical to let two people get their degree based on the same work.

In the PhD theses the publications could be used as such by both PhD, but they need to have a different introduction and synthesis chapter as they worked on different aspects of the joint papers. In addition, I would explain the situation and how the collaboration worked in the preface of both theses.

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  • Sounds very reasonable. – user4423 Dec 23 '12 at 22:50

You should check your department guideline. In mine, only articles where the candidate is first author, and has accomplished most of the work (you need to provide letter signed by other authors) can be used. Also, it can only be used in one thesis.

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  • Thanks for the note, this makes total sense. Unfortunately, the issue is not mentioned in my department guidelines. – user4423 Dec 23 '12 at 22:36
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    Then I would discuss this with your supervisor, maybe even someone higher up in the department to get clear how your university deals with this, just to prevent any trouble. – Paul Hiemstra Dec 24 '12 at 7:51

One case of this that's getting a bit old but was highly influential in artificial intelligence was Phil Agre and David Chapman (PhDs at the MIT AI Lab in the late 1980s). They did everything together, but wrote completely different dissertations. They agreed in advance how they would divvy up the output.

Since a PhD has to have a novel contribution, I think this is the only way it can work. You specify your contributions in the introduction and conclusion, and these can only be contributions by one person, for one dissertation.

Personally, I had a little bit of overlapping text in two of my dissertations (which for bizarre reasons came out nearly the same time), but it was only the literature review, which at the time I didn't think of as a contribution, and I clearly stated the overlap in the later dissertation. Also, I didn't claim that the thing I was best known for at that time (an action selection mechanism) was a contribution to either dissertation, just to be certain there could be no claim I'd made overlapping contributions (One was in Psychology & one was in Systems AI, so they really were pretty different.)

Basically, by the time you are ready for a PhD, you should be able to make any number of contributions. So being productive and publishing articles is the main thing to worry about, and then secondarily following through, and following the rules, so you get your degree. Your dissertation is not a documentation of your life's work – it's just one coherent document making a very clear academic contribution. Hopefully two good students working together would make more than enough contributions that they can divide them up and each write interesting dissertations.

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In math at Berkeley this varied by advisor. Some advisors insisted that theses consist only of solo work, while others did not. My thesis consisted almost entirely of collaborative work (though with different collaborators), and I think one chapter may have also appeared in a collaborator's thesis. The advisor shouldn't sign off on the thesis if the student hasn't done enough work to deserve a PhD, but if you're going to do most of your work collaboratively after grad school it makes sense to me to do so during grad school.

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