At Columbia, PhD defenses are generally not public, although CS usually allows a student audience. Defenses consist of four parts: first, the candidate introduces themselves, then presents a summary of their work, interrupted and followed by questions from the committee. Finally, the committee meets in private to discuss the presentation and dissertation.
While most of the committee will have read most of your thesis, you cannot assume that everyone has read every chapter.
The committee needs to be able to assess impact and depth. Usually, the committee has some idea of this before the defense, but whatever the student can say to make this assessment easier, perhaps just through emphasis, is likely to make the defense go much more smoothly.
Generally, the whole defense will not take more than two hours, but should take considerably less time. Part of the challenge of a defense is to convince the committee that you can summarize the important points of your work in a very limited time.
- Your presentation (and thesis) needs to address the following:
- What is the problem you are studying?
- Why is it important ?
- What results have you achieved?
- Some committee members will want to know if the works has been published and where and how it was received. For example, if you have written software, indicate where it is being used, either for follow-on work or in some production or test environment.
- Have a list of your thesis-related publications as a slide. Indicate any awards that a paper may have received. For most people, it’s easier to list some honor than “brag” about it in person.
- If you have presented your work in a conference or at job talks, be sure to anticipate and address the most common questions asked there.
- The committee should be handed a copy of your slides.
- Be prepared to briefly summarize your background (undergraduate degree, how long at the university, etc.)
- No more than 30 slides, plus “back up” slides with additional material in case of questions. The most effective way of making your committee members mad is to come unprepared with a stack of 80 slides and then madly skip through them.
- Number your slides, particularly if one of your committee members is linked in via speakerphone. Consider using some kind of remote presentation software.
- List your contributions early.
- When presenting your contributions, be sure to use “I” and not “we” so that the committee will know what aspects of the work where yours, and which were group projects.
- Keep discussions of related work very brief, but be prepared to answer questions of the “how does this differ from so-and-so’s work” succinctly.
- You will not be asked to prove results again.
- Be prepared to back up any comparative statement with facts, in particular statements like “works better”, “faster”, “scalable” or “optimal”. If you are presenting a protocol, how do you know that it works correctly?
- If you have multiple parts in your dissertation, consult with the committee ahead of time as to whether it makes sense to omit some of them for the presentation.
- It is better to focus deeply on a single area then to work on several topics, each of which is pursued to a moderate depth.
- Systems work must be coupled with implementation and some kind of numerical comparitive analysis to demonstrate the improvements from existing or alternate approaches.
- Your thesis needs a one page executive summary that a layperson should be able to understand. Test: give it to a relative of yours that does not have an engineering degree.
- You are likely only to defend a PhD thesis only once; your defense is a special occasion, so consider dressing appropriately, at least business casual, but a suit is not inappropriate.
- It is customary to provide refreshments for the audience, such as coffee, bagels, cookies and fruit, depending on the time of day.
The Role of PhD Committee Members
- Committee members (should) read the draft thesis (and provide feedback). Obviously, students appreciate an in-depth reading, but it is common for committee members to focus on chapters closest to their expertise. Reading depths varies – some provide line edits, others just suggest larger issues that should be addressed (“Your related work section in Chapter 10 is a bit sparse and ends in 2005.”). While this is probably not the place to suggest “do another year of research”, filling in gaps is ok and I’d rather postpone a defense by a month if needed. Before the committee gets the thesis, I’ve done a first or sometimes second reading, but the whole point of the committee is to keep the advisor honest (and complement his or her knowledge or taste).
- Committee members attend the PhD defense, usually in person. Typically, this lasts about 90 minutes. Take notes on any editorial improvements (e.g. “make clear that the throughput graph is measured in gallons/minute”). Vote on the outcome and sign the form.
- If the student is given a set of changes to implement, the advisor asks students to detail on how they implemented the changes, similar to how an author may respond to reviewer comments for a journal. The committee informally signs off, or not, on these changes. There is no need to re-read the thesis.
Before you submit your draft to the committee, be sure to verify that you have done the following checks:
- Spell check;
- Check for missing chapter or figure references;
- Section, Chapter, Figure are capitalized;
- All references converted from  to [1,2,3];
- Consistent capitalization in captions;
- Verify expansion of all abbreviations at first instance;
- Avoid “tremendous”, “huge” and other similar adjectives;
- End to end -> end-to-end;
- Check references for capitalization of abbreviations and missing data such as page numbers.
(Contributions by Ed Coffman, Jonathan Rosenberg and Sal Stolfo.)