My PhD Viva

I had my PhD Viva at the end of November 2017. In this post, I’ll talk about what it was like, what preparation I did for it, what questions were asked, and any other information I think might be useful.

My PhD was in molecular, lifecourse and genetic epidemiology at the University of Bristol, and lasted for 4 years. The first year consisted of 3 mini-projects, which each took about 3 months, followed by 3 months of preparation for the following 3 years, mostly refining my plan for the research I would conduct.

My research mainly looked at whether body-mass index (BMI) was associated with prostate cancer and/or prostate-specific antigen (PSA). The aim was to see if, by precisely estimating the associations using previous data, I could make PSA testing for prostate cancer more accurate. PSA testing needs to become more accurate to be clinically useful – presently, about two-thirds of men with a high PSA level don’t have prostate cancer, which means many men have prostate biopsies who don’t need them. I’ll write more about my PhD later I’m sure.


PhD Vivas are probably one of the more stressful experiences of any PhDs life. But before the Viva can take place at all, the student needs to write their PhD thesis, a write-up of all they did during their PhD (or, at least, the bits that they want to talk about). When a PhD student is writing their thesis, it is usually best not to ask when it might be done (by the deadline, hopefully), how they are getting on (not well), whether it’s fun (it’s not) or whether they have any free time (they don’t). Lots of students get very stressed during the thesis write-up, but in general I imagine the better the supervisor, the more stress-free the experience (my supervisors were great).

My thesis had a word limit of 80,000 words – I ended up using about 65,000, with an extra 20,000 words in my appendix. In it, I gave an overview of the prostate, prostate cancer and PSA testing, a description of the methods I would be using in the thesis, and then 5 chapters detailing individual pieces of research, which led to a final discussion chapter. It took a while to write – I wrote as I went along, but it was still 3 months or so of editing and adding new content at the end to get it to the final copy. I’ll talk about the thesis later – lots of PhDs I know have had trouble knowing what to do for it and when, so I will write about my experience.

Once my thesis was complete, I posted two copies to my two Viva examiners. Because I had worked in my department before and during my PhD, I had two external examiners – two academics in related fields who were chosen by my supervisors to assess the scientific merit of the work I had done. Usually, PhDs have an internal and external examiner, i.e. an examiner from the same university (although hopefully unconnected to the student, otherwise there could be bias), as well as someone from a different university. As it happened, one of my examiners didn’t receive the thesis, and my supervisor had to email them a copy (note to all PhD students: have your supervisor check you external received your thesis).

My examiners had over a month to read my thesis and make comments on it. This task can not have been fun – 65,000 words is the size of a small-medium novel, but written in the dense, complicated style of a scientific journal article (which tend to be 2,000-3,000 words in my experience). It’s also a fairly unrewarded task – I think the examiners might receive a small fee and any expenses, but nothing like what would cover their time reading the damn thing. So I offer huge thanks to my examiners, and all examiners too.

After submission, I had a week off. I started a job after that, but it was in the same department working with the same people, and it was a job specifically created for PhDs to write up parts of their thesis for publication in journals, revise for the Viva, and conduct some new research. It is a great job, and gave me time to revise for my Viva. In total, I had 2 months between submission of my thesis and the Viva.


In those two months, I can’t say that I did as much preparation as I could have. I think I read through my thesis once. This is always a painful task, since you inevitably notice typos, errors, and just generally unclear bits. But it needs to be done so you can talk about everything you did in the thesis. So I made notes of what I needed to change after the Viva, as well as any bits I needed to revise.

I looked up typical questions that are asked in most Vivas, and jotted down some answers. Mostly, it was along the lines of “which methods did you use and why, and which others could you have used?”, and “what potential impact will your research have?”. My supervisors had me write a detailed 2-3 minute talk about what I did and rehearse it, just in response to the most common opening question – what did you do? One piece of advice I received was to nail 5 key points, and have a couple of optional extras in case you need them. This was good advice – the first question was indeed to describe what I did.

The Viva itself was to test 3 things (or so I’ve been told): 1) did I write the thesis; 2) do I know the science behind what I did; 3) is the science any good? The first and third points I had little concern about – I know I wrote the thing, it took up a large chunk of my life and I went through it before the Viva – and I knew both that the methods I used were valid (I published a paper using similar methods during the PhD), and that my supervisors are good at what they do. If there were any problems they would have spotted them, and anyway, there was nothing I could do about the science once the thesis has been printed.

That left the second point, and the one I focused on the most. While I have a good grasp of systematic reviews and meta-analyses, two techniques I made extensive use of in my thesis, I also used Mendelian Randomization (which I have used less and am thus less confident with), and several statistical methods that I could explain in simple terms but would be stumped to go into detail with. I therefore spent time reading through anything I was unsure about – this turned out to be almost completely unnecessary, but I would say that it was likely worth my time revising those concepts anyway.

At the end of the Viva, the examiners make recommendations to the exam board, which determines whether the students passes, and if so whether they need to make any corrections. Pass without corrections is rare in my department (1-2%). Minor and major corrections account for almost all Viva results. These are both still passing grades, the difference is the degree of time required to get the thesis up to a standard the examiners would like. Minor corrections should take less than a month to make, whereas major corrections could take up to 6 months. If someone is working, this could be taken into account and major corrections given so the student has more time to work on it. Rarely, but sometimes, the examiners recommend the student take a year to redo their work and resubmit – this is not a passing grade. There may be worse outcomes, but these would be vanishingly rare in my department. All examiner recommendations go to the exams board, which has the final say, but I don’t know in what circumstances they would ever not go with the examiner recommendations.

My Mock Vivas

My department are great – I had two mock Vivas before the real thing. These were two hour-long sessions where professors and researchers read through specific chapters of my thesis and grilled me on them. This was both good practice for being grilled (although as an academic, I’m fairly used to that from supervisor meetings, conferences and other presentations), and finding any weak parts of the thesis that need my attention.

They were set up as close to the real thing as possible. The mock-examiners met in a room and discussed what they would ask and how, then I was called in. They asked about what I did in general terms, then went through the chapters in question systematically, asking why I did things, could I have done them other ways, pointed out issues and made recommendations if appropriate. At the end, they gave some feedback.

After the mocks, I felt more prepared, because I could answer most of their questions well enough to satisfy both myself and them. However, I was talking to a friend who did their Viva shortly before me, and they felt that if they had a mock that went poorly, their confidence would have been shaken for the real thing and they would have done worse.

As it turned out, my mocks were in fact much harder than the real thing.

My Viva

My Viva started about midday. That morning, I read through key parts of my thesis and thought through some questions that might come up, but generally took it easy. I arrived about 10, bought some lunch, and found a quiet place to revise.

Because I had two external examiners, I also had an internal chair, someone to do the introductions and make sure everything is above board. I managed to catch them as they went in with the examiners for lunch and let them know where I’d be, so they could come fetch me when they were ready.

About half an hour after they went in, I was collected. After a quick introduction, the examiners took turns to ask me questions. It started with the general “what did you do?”, and progressed from there. The difficult questions that came up in the mocks made no appearance – what I remember talking about most were the new methods I developed in order to do my research slightly better, which happened to be the bits I enjoyed the most and liked talking about. There were a few things I had to change to satisfy them, but mostly this was putting work back into the thesis I had taken out, thinking it was too much detail. Overall, it was a pretty enjoyable experience, and was over (apparently) quite quickly – all told, I was in there about 1 hour 40 minutes.

Once over, the examiners asked me to leave while they had a discussion, and I was shortly called back in to be told I passed with minor corrections. We then made some awkward chitchat – my supervisors were coming to talk to (and thank) the examiners, but had planned on me being in there longer. However, everyone eventually arrived, more chitchat was exchanged, and we all left feeling quite happy.

My supervisors and I went for hot chocolate afterwards.


I’ve spoken to a few people about their Viva. Some enjoyed it, some hated it. Examiners can be great (mine were lovely), or they can be awful (someone said their examiners were known for asking extremely awkward and difficult questions, which isn’t really the point). I think the fear of the Viva is a bit disproportionate to the risk of failure – it’s true that it’s a very important exam, but so long as the supervision has been good and the supervisors are happy with the thesis itself, then there should be little risk of failure. Examiners (in general) want you to pass. And problems with the science (I admit complete ignorance of non-scientific PhDs) can be fixed in corrections. Some people will of course fear talking about their work in front of strangers for two hours, in which case practice may help (as does having a supportive department – I’ve heard of professors slamming student’s work in seminars; this is not constructive).

I think the Viva can be also something of an anticlimax for many students. A PhD in this country usually takes 3 years, mine took 4, and a thesis can take months to write. There can be months of waiting between submission of the thesis and the Viva, and then hours to wait on the day. Then the Viva happens, and it goes pretty quickly. Then it’s done. Years of work, judged in a couple of hours. And then you’re a doctor, hopefully (although I’ve never actually found out when you legitimately become a doctor, probably after graduation). Still, the relief is good.

So overall, I liked my Viva. The mock Vivas were helpful, if not for the specific questions then for the experience. Preparation was not massively important for my Viva, but could easily be for others – reading through my Viva once would likely have been sufficient, but I may have felt woefully unprepared then. And examiners should definitely be thanked, often and well.

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