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I am working on writing my PhD thesis after four long years of work. I'm writing the hypothesis sections, and I am finding it extremely hard to write one single hypothesis that is comprehensive and specific enough without using vague wording. Can I have three hypotheses for my thesis?

For background: my work is in medical informatics, and my thesis work can be divided into three steps:

  1. I evaluated existing models in the literature against our hospital's dataset using a novel approach and demonstrated that their performance is not great;
  2. I developed my own model, which is better;
  3. I implemented it in the hospital, with decent results.

Can I have those three as hypotheses? [1) existing models perform worse than X; 2) a model that is X% better can be built using machine learning; and 3) implementing a model in the hospital can lead to XYZ]? Or do I have to find just one overarching hypothesis and make those three the goals?

  • 1) Consult with your advisor. 2) That looks like one project, and projects just naturally are done in steps. So you designed a model, that turned out to be better than other, and successfully implemented it in a real-life situation. – user68958 Sep 3 '18 at 20:18
  • That sounds pretty typical in my fields, which is at least medical adjacent – Azor Ahai Sep 3 '18 at 22:03
  • Sidenote: “a model that is X% better can be built using machine learning” – I would remove “X%” here. You certainly didn’t have any numbers in mind when you started working on this. – Wrzlprmft Sep 4 '18 at 6:48
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This is the sort of thing that you should discuss with your advisor if you have questions. This may be field specific; that said, I'd be surprised if there was any sort of specific limit on the number of hypotheses discussed in a thesis.

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You can certainly do that, but if you can get your degree with a simpler structure it might be worth doing one thing and use the other work for future papers and such. Your advisor should be a good guide here, actually.

It doesn't sound like you have three distinct things going on, however, and that all three of them support a common overall theme. If the results all point the same way you should have a strong result. Your number (2) seems like the big thing, with (3) supporting it and making it concrete, though I don't see how you support (2) without (3). Not my field, though. But (1) would be a pretty common element of a dissertation.

That sort of thing is pretty common actually in many fields.

I would only recommend against a number of hypotheses if they were disparate in some way.

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