Surviving, and maybe enjoying, your thesis defense

It’s the big day. Today, you defend your thesis. So what can you expect?

There are variations in the format of the thesis defense from university to university, and certainly from one country to another. What I’m going to say is necessarily going to apply most directly to the system we have here at the University of Lethbridge, which is similar to what you would see at most North American universities. But I think there may be elements of this post that will apply no matter where you are. With that caveat in place, I’m going to focus mainly on the questioning phase of the thesis defense.

What to bring to your defense

If your defense is to start with a presentation, make sure you have your presentation on a memory stick or two, and in your email, and maybe in some other backup place so that you’re sure to have it when you get there. It is likely that chalk or whiteboard pens will be provided, but it doesn’t hurt to have a piece of chalk or a whiteboard pen in your pocket so you can generate a quick sketch or write down an equation in the course of answering a question. If possible, check out the room first so you have some idea of what the audiovisual situation is going to be, including what kind of boards the room has.

I strongly recommend that you bring a printed copy of your thesis. The defense proper is normally conducted around some kind of table. In our case, defenses are usually conducted in classrooms, so we do our best with furniture that isn’t quite right for the purpose, but in any event you will likely be sitting for most of the defense. The examiners will invariably want to refer to specific pages of your thesis, and expect that you will have a copy on hand. I personally think that flipping through the pages of a physical copy is easier than dealing with an electronic copy, but that’s a personal choice. Either way, you need to be able to refer to a copy of your thesis during the examination. By the way, you shouldn’t count on being able to plug in a laptop in the thesis examination room. There may or may not be available outlets. Don’t take anything for granted. Charge up your device(s) or, again, bring a printed copy. You can’t go wrong with paper.

The opening presentation

Depending on the system at your university, the questioning may or may not be preceded by a presentation, which may or may not be open to the public. There are just too many variations on this theme to properly address it in a blog post. If you do have to make a presentation, tell yourself that your main audience is the examiners, who are likely to use what you say in your presentation as a springboard for questions. The same comment therefore applies to your presentation as to your thesis: Don’t say anything in your presentation that isn’t completely clear in your head.

Ready for the questions?

Because here they come! You can expect many types of questions, sometimes interspersed with comments, some of which I mentioned in my previous blog post.

  • There are likely to be some direct technical questions about the contents of your thesis. “What did you mean by that?” “Could you explain the logic behind this part of your thesis?” “Explain how technique A, which you used in your thesis, works and how the results are interpreted.” “Walk us through the analysis of experiment P.” And so on. As I explained previously, you almost always need to be able to answer these questions.
  • There may be criticisms disguised as questions. These pseudo-questions often sound like questions from the first category. For example, an examiner may ask a question about your use of terminology, or about an assumption you made. The examiner already knows that you will give an answer that violates some orthodoxy within which they work because of what you wrote in your thesis. They will then explain to you the error of your ways. Some examiners will dispense with the pseudo-question and just tell you outright that there is an error of some sort in your thesis. You need to be mentally prepared for these events, which are fairly common, although not typically a major component of a defense. Showing some understanding of the issues once they have been explained to you is good, provided of course you do understand the issues. Humility is absolutely required. Do not argue with the examiner if they tell you that something you wrote is wrong. Even if you don’t think it is, the examiner is at least pointing out something in your thesis that is liable to misinterpretation and that therefore needs to be clarified. Do ask questions if you do not understand the examiner’s point. Other than asking to have questions clarified, on which more below, this is the one situation where you will likely be allowed to ask questions during your defense.
  • Examiners may make suggestions about revisions to your thesis. Many students are tempted to take notes when this happens. This isn’t necessary. You will be provided with lists of suggested and required revisions from the examiners after the defense.
  • There are likely to be questions about where your thesis fits into the overall scientific enterprise. Why is your work important? How does it connect to other open questions? What new insights do we get from your work? There should already be material along these lines in your thesis, particularly in the introductory and concluding chapters. The examiners will likely want to go a bit deeper than what you wrote. You should be able to take a stab at questions like these although, on occasion, the questions will veer off into areas of science you really know nothing about.
  • Someone will almost certainly ask about what the next logical step in your research would be, were you to continue this line of research. Again, you need to be able to give some sort of answer to a question like this. Ideally, you would have answers to such questions that go beyond trivial “one more experiment” answers, and that show that you have a vision for your field of research.
  • You may be asked to revisit your work, i.e. to think about what you might have done differently, given what you know now. Usually these questions are fairly specific. “You used method B to determine property X. Are there other, possibly better ways you could have done that?” It’s great if you can answer these. You don’t have to constrain yourself to the facilities you had access to during your degree. Go ahead a propose a cool cyclotron experiment! If you really can’t think of an answer to one of these questions, an examiner may offer a suggestion and ask you to comment. Typically, an examiner would not be drawing on obscure knowledge to frame questions like these, and you should be able to provide some intelligent comment on what you would have learned (or not) from a different method.
  • On occasion, you will get an examiner who likes to steer the conversation towards their area of research. Unless the examiner’s area is very close to yours, this can get you into deep waters fairly quickly. Bonus credit if you can give a sensible answer, but it’s probably OK if you can’t answer these questions in much depth.

How to answer questions at your defense

Rule number one is: think! You don’t have to blurt something out instantly. Take a few seconds to compose your thoughts. Make sure you understood the question. If you’re not sure, ask for clarifications.

Rule number two is that answers to technical questions should be technically correct. You should understand the experiments or calculations you did thoroughly. You should know the key scientific theories, methods and observations from your field.

Rule number three is don’t overinterpret the question. Not all of the questions will be ultra-sophisticated. Remember that some of your examiners may be from a different field, and may have very simple questions. Even examiners in your own area may want to ask you a simple question, either to help you relax towards the beginning of the defense, or to set up a deeper question. Listen carefully and answer the questions that were actually asked. Don’t look for complex interpretations of simple questions. You would be surprised how often students fail to answer questions satisfactorily because they are interpreting a question in the most complicated way possible when an examiner was really asking a very simple question.

Many of the questions will invite you to speculate. Rule number four is that speculation should be based on sound science, but that it’s OK to extrapolate, even into areas you’re not comfortable with. You should however make it clear when you are doing so. “I’m not an expert on X, but I know P and Q, so I think perhaps T will hold.” Interesting conversations often evolve from such questions and answers. The examiner may give you additional information and ask you to incorporate that into your thinking. Again, give yourself a little time to think, and then tell us something interesting.

But what if I really don’t know?

Then say so. (I guess this is rule number five.) There may be questions that you genuinely don’t know anything about. Don’t try to bluff. That will end badly. Just say you don’t know. Depending on the nature of the question, any of the following may occur:

  • If the examiner knows that the question is really a stretch, they may simply move on.
  • If it’s a question the examiner thinks you should be able to answer, they may try to rephrase it, or to give you a hint about what they’re looking for. Listen carefully. Try to keep calm and to process the information provided in the question or hint. Think. Hopefully it will become clear what the examiner wants and you can proceed to answer.
  • Examiners often come to an exam with a set of related questions that build on each other. If you fail to answer a question that is part of one of these sequences, they may provide you with an answer so that they can carry on with their line of questioning.

Be aware though that you are expected to answer most of the questions. If you answer “I don’t know” more than once or twice, you’re usually in trouble. What examiners are looking for, above all, is intelligent engagement.

What happens after the examiners send you outside?

Once the questions are finished, the examiners will send you outside so they can deliberate. This can take anywhere from 10 minutes to an hour. What exactly the examiners have to decide depends on the rules at your graduate school, but typically there are two questions, whether they are evaluated separately or not:

  1. Was your thesis, on the whole, acceptable?
  2. During your oral examination, did you show an adequate grasp of your project and of your area of science?

Your thesis should have been read and extensively commented on by your supervisor before you submitted, so in most cases, it will be found acceptable, but expect to be asked to make revisions. It is very rare that the examiners don’t find at least a few passages that aren’t as clear as they could be, or some particular issue that you glossed over. In some cases, they will have more serious concerns about some parts of the thesis, and you may be asked to make major revisions.

If deliberations go on for more than 20 minutes, it’s usually because major deficiencies were identified during the defense. You either said “I don’t know” much too often, or you gave incorrect or badly incomplete answers to more than a few questions. In these cases, the examiners need to decide if they want you to do it again, possibly after revising the thesis. Deliberations that are dragging on are a sign that the examiners are having trouble agreeing. They will eventually vote, but if you had a weak defense, the discussions are much tougher and more drawn out because everyone wants to make sure they do the right thing in the end.

Of course, most of the time—and I want to end on this note—the thesis needs only minor revisions, and the defense went well enough that there is no real controversy about giving you a pass. Congratulations. You can now move on to the next stage in your life. Or at least you will be able to do so once you complete those revisions. But tonight, go out and celebrate. You can start working on the revisions tomorrow.

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