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I'm writing up my physics PhD thesis, and am wondering whether to include the derivation of a formula that I worked out myself. I've recently found that this work isn't actually a novel contribution to the field, as the formula (though not a detailed derivation) appears in the appendix of a 10 year old paper.

Is there any sense in including it? And, if so, how would one describe the contribution?

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  • Absolutely include it! You should cite the 10 year old paper of course, but I would feel free to write that you discovered your derivation independently, and to highlight anything interesting about your derivation that isn't in this other paper.
    – Anonymous
    Commented May 25, 2015 at 11:46

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There is usually no reason not to include something in a thesis. Your thesis is a place for you to give a coherent account of all your work on a topic. There are (usually) no page restrictions, and it should serve as a reference document for future readers.

Many theses include a lot of review material, beyond just what might be contained in a literature survey. A thesis has to contain new material, of course, but it does not all need to be novel. There can be a lot of merit in giving detailed explanations of known results, if the reader is not necessarily going to be familiar with them in detail. A derivation that has not previously appeared in the literature (even if the final result is known) is clearly suitable for inclusion.

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    "There are no page restrictions" - For some Universities, plain wrong. Mine has a limit of 300 pages for the PhD thesis, and less for a Masters or Bachelors Degree. The reality is that this varies from university to university.
    – DetlevCM
    Commented May 24, 2015 at 13:40
  • Yes, some places have, in principle, page restrictions. However, they are uncommon, and I have never known a student in a technical field (the questioner sounds like they're a science or engineering student) who was anywhere close the institutional limit of thesis length.
    – Buzz
    Commented May 24, 2015 at 14:17
  • In my case there is a word limit of (I think) 65k words and I'm at no risk of even approaching that. Should I choose to include it, I'm still unsure how to present the work. Here is a derivation... oh, and it turns out this was first published [here]. Or start with a reference to the earlier paper and then make the case for including it.
    – amn41
    Commented May 24, 2015 at 14:49
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    @Buzz I'm in engineering - still have a limit. - Now the limit can be extended if this is necessary, but that needs permission from "higher up". The aim here is to make sure people write about what is important and don't waffle. It is better to write a good 150 pages than a useless 300.
    – DetlevCM
    Commented May 24, 2015 at 17:51
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    I would argue that a derivation should be included iff it is non-trivial (basically almost always). A PhD (I'd even say Masters) thesis should be self contained and contain all the gory details of the work such that anybody reading it could take off where you stopped.
    – Nox
    Commented May 24, 2015 at 21:01
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This is one of these case which very from country to country - from University to University. For example a German PhD is very different to a UK PhD, in how it is handled, evaluated etc.

For the UK, obtaining a PhD is easiest if:

  • You have made a novel contribution to research
  • That contribution is publishable/has been published

However, sometimes things go awry, you cannot afford equipment, your institution lacks the ability to do research etc. so you can also obtain a PhD on the basis of

  • a systematic in depth investigation of your research topic with a sufficient amount of sufficiently high quality work

Now coming back to the contents:

As a most simple description, a PhD Thesis should be a scientific document that is on its own understandable to an averagely educated person. So non specialist school level knowledge may be assumed as a priori known while specialist concepts should best be introduced in greater detail. Then again, some people do not include a large literature review or large background review while others do, this varies from country to country, from institution to institution.

The best advice I would give you is:

  • IF the information is of direct relevance to your work and required for an understanding of your work and is not trivia it would be better to include it in the thesis as background to aid the reader.
  • IF the information is trivia in another field but not yours, it would again be beneficial for readers to have that information as opposed to having to seek it out.
  • Check with how your institution likes its theses, do people generally write an extensive literature/methods review (in which case you should possibly include it) or do they just tend to write a rather plain presentation of results (in which case the benefit may be debatable).
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    I have never encountered or heard of a maths PhD thesis which was 'on its own understandable to an averagely educated person', nor do I think it would be acceptable to include material explaining a thesis topic to someone who knew calculus, but no undergraduate math.
    – jwg
    Commented May 25, 2015 at 7:33
  • @jwg That is the ideal though. PhD Theses are aimed at a general audience while papers are aimed at a specialist audience. If a university lets someone get away with writing a PhD Thesis for a specialist audience only then that's how its done there - it isn't ideal though.
    – DetlevCM
    Commented May 25, 2015 at 11:49
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    PhD Theses are aimed at a general audience — [citation needed] I have never heard anyone express this aim before. I have also never read a single PhD thesis that even attempted to aim at a general audience. What field are you in that has such accessible PhD theses?
    – JeffE
    Commented May 25, 2015 at 16:48
  • @JeffE Engineering in my case - as far as I am aware though this holds true for all Natural Sciences. A PhD Thesis is NOT written for a specialist audience, that's what papers are for.
    – DetlevCM
    Commented May 25, 2015 at 17:55
  • @DetlevCM My experience in a strong college of engineering is entirely inconsistent with your advice. Again: [citation needed]!!
    – JeffE
    Commented May 25, 2015 at 17:57

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