We had an interesting discussion at lunch last week, about the fact that many PhD students are very nervous about their viva (oral exam after submitting their thesis), despite the fact that its very rare to fail a viva. That is, while only a small number of students have reason to worry, we see a lot of students who are very stressed and worried despite being very unlikely to fail.
So here is my thoughts on which students are likely to pass and which may have problems; hopefully this will reassure the majority of students who will not have problems!
Note that I am talking about students who actually submit a thesis. Some students decide a PhD is not for them and drop out; I’m not talking about such people here. Also I’m focusing on the UK system, other countries have different PhD processes, but I think similar factors apply.
Failing a Viva
In the 20 years I have been examining PhD students, I only once failed a student completely. This happened when I was external examiner at another university (call it University A), it did not happen at Aberdeen!
Anyways, in this case, as with most failures I am familiar with, the problem was poor supervision. The student had come to University A to work with Professor X. However, Professor X then accepted a second appointment at University B, which was several thousand miles from University A. In theory he was supposed to split his time between University A and University B, but in practice he spent almost all of his time at University B, and was rarely seen at University A. Which meant that the student almost never saw his supervisor (this was many years ago, when video-conferencing was still an expensive rarity rather than an everyday occurrence).
What should have happened in this case is that University A should have appointed a replacement or second supervisor for the student, since Professor X was never around. But they did not, so the student effectively did not have a supervisor. And without guidance from a supervisor, he was unable to make progress towards a PhD.
Anyways, this is obviously an extreme case, where the student had effectively been abandoned by his supervisor, with no replacement supervisor.
Advice to students before a viva: If you have good relations with a supervisor who you see every week or two, and your supervisor has agreed that your thesis is ready to be submitted, then it is very unlikely that you will fail the viva.
At least in the UK, PhD students can be asked to make major corrections to their thesis (which could take another 6-12 months of work), and then resubmit it and have another viva. This happens when the examiners think the work is not good enough for a PhD, but can be salvaged.
I have been involved in a few such cases over the years, and usually it is a result of either a weak supervisor or a weak student. Some supervisors simply do not understand a field well enough to supervise a PhD student. Its usually easy to identify such supervisors by checking their publication record (eg, via Google Scholar). If someone is regularly publishing papers in a field, then he is probably knowledgeable. If his last relevant publication was ten years ago, then he may not be knowledgeable. My advice to PhD students is that they should check the publication record of a potential supervisor, and look for alternative supervisors if the publication record is poor. It will only take 10 minutes, and may save you a lot of grief.
The other cause of major corrections is weak students, that is students who for some reason (perhaps personal circumstances such as health issues) struggle to make good progress on their PhDs. One indicator of a weak student is a lack of publications. If you dont have *any* publications when you submit your thesis, this is definitely a warning sign! On the other hand, if you have one or two papers accepted at good conferences or journals (especially if these are full papers on the normal track, not short papers or student-track papers), then you are not a weak student!
Advice to students before a viva: If your supervisor is regularly publishing academic papers, and you yourself have at least one full paper accepted at a good academic conference or journal, then it is unlikely that you will be asked to make major corrections.
Most students are asked to make minor corrections. Ie, the thesis is basically fine, but the examiners want it to be tweaked a bit. If you are asked to make minor corrections, then congratulations, you have passed! In theory it is possible for a PhD thesis to be accepted as submitted, but in my years I have never seen this outcome; so minor corrections is as good as it gets!