Has a "portfolio" of orthogonal projects ever been acceptable for a PhD thesis, instead of a single large project?

Question

My interests are very broad. Before grad school I did a lot of things, but now it's expected that I only do one thing. Provided that I can demonstrate research competence in more than one field, by publishing for example, is it possible to write a thesis that consists of several smaller, orthogonal projects instead of a single great push? I understand why this isn't encouraged - diluting yourself is not an efficient way to get things done and it's unlikely that one would be able to become a PhD-level "expert" in more than one deep subject. But provided that one is very industrious and willing to give up the prospect of having any kind of normal life, which I am, has this ever been done?

Also: I realize this is funding-dependent - assume that I have external funding from a fellowship.

Many PhD students already give up the idea of a "normal life". — , Feb 25 '18 at 09:30
It depends a bit on the field in my opinion. Departments that are a mix of life science and engineering/physics tend to be very interdisciplinary in which case a diverse thesis might be acceptable. — phimac, Feb 25 '18 at 10:53
What's the story of your thesis? If you have three themes that build a single story, it may work. If you have three themes that are, well, three themes, then you have three little sub-theses, but not a thesis. — Captain Emacs, Feb 25 '18 at 12:39

score 5 · Answer 1 · answered Feb 25 '18 at 10:19

It will depend on the advisor, the university (i.e., will they allow you to work in different fields. I mean, technically they can't forbid you to work on something, but your advisor might not be pleased with it) and the details of the topics (will it be really possible to work on a variety of them).

In general, a thesis should provide an answer to a research problem, either in the form of a self-contained book, or a sandwich thesis.

I'm also interested in many fields (which can be divided roughly into 3 main ones at the moment) that are not really connected to each other that much. My advisor told me to compose a thesis only about one of the topics (which I published 3 papers on), and not to make a mix of unrelated works (sounds reasonable to me). And that's how it was done (in the form of a sandwich thesis).

I added the papers on other topics to my CV, and they were useful when applying for a grant, scholarship etc. And of course for conference presentations.

score 2 · Answer 2 · answered Feb 25 '18 at 09:37

Ultimately, it is the University's decision what call a PhD thesis. While the widely accepted norm is indeed a large piece of independent work on a single question / topic, a "portfolio" of small but important contributions can be accepted in exceptional cases. These exceptions, however, are justified by the exceptional quality and importance of the work done, clearly demonstrating the candidate's expertise, skill and talent. Simply having family and kids is unlikely to be sufficient for the exception to be made.

Has a "portfolio" of orthogonal projects ever been acceptable for a PhD thesis, instead of a single large project?

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