Dr. Andrew Broad
Computer Science
Nasty PhD Viva Questions (Extract)

A PhD candidate needs to anticipate the questions that are likely to be asked in the viva - the "horrible ordeal where you have to defend your thesis in person before they rip you to shreds." Actually, it's not nearly as bad as it sounds, provided that you enter it having prepared to your utmost.

There are three reasons why PhD candidates have to have a viva: it is so the examiners can see:

These are the points being examined (according to Alex Gray from the University of Cardiff):

Preparing for the Viva: Before you submit

It's crucial to get the philosophy of your thesis (as set out in your Chapter 1) absolutely correct, and clear in your mind by the time of the viva, because if the examiners find holes, they'll run rings round you.

They could ask you to explain/justify any statement in the thesis, so beware of baring nasty branches for clarification at the viva! Identify the contentious statements in the thesis, which you anticipate having to defend in the viva. A good supervisor will point out the contentious statements and grill you over them. Start a file of anticipated viva questions.

The conclusion chapter is a major one to focus on in anticipating viva questions - especially where you criticise your work!

Obviously, it's essential to know your own thesis thoroughly. I think it's a great idea to compile a brief summary of each section before you submit - enough to remind you of what's in each section, paragraph by paragraph or similar (my thesis summary is very different to, and shorter than, my thesis plan, where I basically wrote down all the points I could think of, then when I wrote it up, I added and deleted points, and changed the structure). Compiling a thesis summary before you submit has the advantages that you may spot strategic-level flaws in time to fix them, and will enable you to revise for the viva from the thesis summary rather than from the thesis itself.

Don't try to get the thesis perfect and free of minor corrections at the expense of delaying submission. It's almost certain that the examiners will find something to correct, anyway.

Preparing for the Viva: After you submit

The most important goal in preparing for the viva is to keep the subject alive in your head.

Try to anticipate the questions you'll be asked in your viva and keep working on a file of anticipated questions (both the generic questions listed on this web-page, and questions specific to particular sections of your thesis) and your answers. If you said anything without understanding it 100%, or anything you have doubts about having justified properly, add it to your viva file.

You can go into university after you've submitted your thesis and your registration has expired - doing some more practical work may (or may not) help to keep the subject alive in your head (you could do experiments and take printouts of the results to the viva).

However, the main preparation for the viva is reading. These are the things to prioritise:

  1. Know your thesis inside-out. Compile a thesis summary (see above) if you didn't do so before you submitted - revising from that rather than from the thesis itself will help you focus on the strategic level (a half-line summary of each paragraph in the thesis should suffice to remind you of every important point in the thesis). You should read your thesis summary in a continuous cycle while you're waiting for the viva, and you should read the thesis itself at least once after you submit it and before the viva. Try to read it from the perspective of the examiners.
  2. Be familiar with the references cited in your thesis, because that's the literature your examiners are most likely to ask you about. Read anything you have cited without reading (not that you should cite things without reading in the first place!).
  3. The examiners could also ask you about literature not in the thesis, to test whether you are widely-read in your area.

It might be an idea to publish a paper or two between submitting your thesis and the viva - I wish I had done so. Try to write papers from different perspectives.

The time between submitting the thesis and the viva varies greatly. I submitted my thesis on 28th September 2001, and had my viva on 18th September 2002! My thesis was very long (390 pages including appendices), and there was a delay in finding a suitable external examiner, but above all you have to remember that your examiners will be busy with other things too!

The shortest time I've heard of between submission and viva is three weeks (different subject, different university).

They have to give you at least two weeks' notice before the viva. I got five weeks' notice. My internal examiner suggested a couple of dates, I chose 18th September and asked for 14:00 in IT406, and this was officially confirmed a few days later.

The Viva itself

The PhD viva is an open-book exam: you can bring any materials you want. Here is what I think one should bring to the viva:

At my viva, I gave a presentation (using slides) about some experiments I did after I submitted my thesis. But it's unusual for the candidate to give a presentation, and your supervisor should advise you if it is appropriate to do this. If you do give a presentation, be prepared to be flexible - I was asked to speed up and just give the highlights.

It is not the norm, in this department (I do not speak for other departments/universities), to be expected to give a practical demonstration of your work at the viva, but you could always offer to do so if you think it will help your cause (unlikely).

Anyone can attend a PhD viva, but only the examiners and the candidate can participate. (This means it may be a good idea to attend someone else's viva before your own, though I've never had the balls to gate-crash a viva! :-o )

Your supervisor should definitely attend your viva, although (s)he is usually not allowed to participate unless invited to do so by the examiners. It might be an idea to keep an eye on the body-language of your supervisor to see if you're going wrong! ;-)

A viva typically lasts two hours (but as long as it takes - mine lasted 2h22m), and a common approach is for the examiners to go through the thesis sequentially, asking questions.

Just because they ask a lot of questions doesn't mean you're going to fail. They don't give away the result before or during the viva, but you may be asked to wait around for the result at the end (about half an hour), so that they can explain the result to you - particularly if you have to resubmit your thesis (failure without the option of resubmission is very rare, and is not going to happen if you submit anything resembling a sensible thesis).


Typical Viva Questions

Here are some generic viva-questions - you should instantiate each question for your particular thesis, and have a framework for answering it worked out before the viva.

I have tried to cluster related questions together here - they are not necessarily in order of importance, nor in the order that they are likely to be asked at the viva.

General Questions

Particular Questions

Most of the viva will probably consist of questions about specific sections of your thesis, and the examiner should give a page-reference for each question. According to Alex Gray, these questions fall into six categories:


Much of the material on this page comes from my supervisor Nick Filer, from CS700/CS710, from questions I've been asked at the end of various presentations I've given, and from my own viva (most of the questions there were thesis-specific). I added questions from the external websites given at the end of this document. I also updated this document in the light of Alex Gray's keynote speech, "Surviving the PhD Viva: An External Examiners Perspective" at the 2002 Research Students' Symposium.

If you can think of any viva-style questions that are not covered by the above, please do not hesitate to tell me, and I will consider them for inclusion on this page.

Finally, I found my own viva much less stressful than I thought it was going to be. The examiners know that it's an ordeal for anybody, so they should go out of their way to put you at your ease and make you feel comfortable. I was amazed how calm I was, even when I went back to hear the result. If you're worried about getting an `impossible' resubmission-order, remember it's not the examiners' job to set insurmountable hurdles - they want you to pass as soon as possible.