What is a Ph.D. Defense and How To Nail Yours


Earning a Ph.D. is no easy task. It involves a lot of time, reading, writing, revising, research, and money. When an advisor and student feel that a student’s thesis has finally reached strong conclusions, it is time to defend it. A successful defense is the key to earning the sacred diploma and is likely something a student only wants to go through once. In this post, we’ll be going over how a defense works and tips to nail yours.

Dissertation versus Thesis

Just like artificial intelligence does with machine learning, the non-academic world often uses words like thesis and dissertation interchangeably. A reminder that a thesis is an idea, while a dissertation is a document that substantiates your thesis.  

Parts of a Ph.D. Defense  

  1. The Introduction – Introduce yourself and your work
  2. Presentation – The core part of your defense. Here you will summarize your body of work. Do not panic if a committee member interrupts you to ask a question!
  3. Q&A – The committee will likely have several questions about your presentation. Other attendees including faculty, fellow students or your own invited guests are also permitted to ask questions.
  4. The Decision – The committee will meet privately to discuss your presentation and thesis. They will also vote on whether or not you passed or if any revisions need to be made before passing.

The Committee

As referenced above, there is a committee involved with each defense. Most students are allowed to select their committee with the help of their advisor. Your advisor is usually a member of your committee.

It is the committee’s job to read your thesis, provide any feedback prior to or during your defense, attend your presentation and ultimately vote on whether or not your work is worthy of denoting you with a Ph.D. Their role is to assess the impact and depth of your work.

While committee members should read your thesis in its entirety, it’s common that they will only read the chapters that pertain to their expertise. When presenting, keep in mind that it is likely that not everyone has read every part of your thesis. Most committee members attend defenses in person.

If you have a lot of parts to your dissertation, it might be helpful to consult with your committee beforehand about which sections to leave out. It is usually best to focus on one issue and do a deep dive versus moderately hitting a lot of points.

The Presentation

Your presentation should last no more than two hours and answer the following questions.

  • What is the problem you are studying?
  • Why is it important?
  • What results have you achieved?

It sounds strange, but do not hesitate to use “I” instead of “we” when presenting your defense, but only when true. This designation helps the committee members know what work you were responsible for versus what was a group project. They are judging YOU, not your group, so now is the time to self-promote and list your contributions early!

It’s a difficult task, but if you can summarize your thesis in ONE sentence, do it. In fact, it’s recommended that you make this one sentence the first sentence of your entire dissertation. This will help keep your dissertation and presentation focused and leave no doubt for what you are trying to prove.

If your work has been published or is currently being used, note that in your presentation. Committee members will likely want to know if it won any awards or how the product is performing. If you presented your paper at a conference, go over what questions you were asked then and be prepared to answer them again for committee members.

If you use any comparative statements like “works better”, “scalable”, or “faster”, be prepared to back those statements up with proof. Committee members will be quick to call you out if you make statements like these and can not provide the facts to prove it.

Your presentation should be no more that one hour, and you should rehearse it at least once in front of your peers. You can have a few extra slides with “back up material” for questions, but the fastest way to lose points with committee members is to fly through a 100 slide deck versus a well prepared, concise deck.

Don’t forget to include a one-page executive summary at the beginning of your thesis. This summary should be written so that anyone could understand it. We know it’s hard to remove yourself from your own work, so have a friend or family member who does not have machine learning experience read it. If they can’t understand it on their own, it is too technical.

After sending the final dissertation to the committee, you should not make “improvements” to the text, either in the thesis itself or in passages that are quoted in the presentation. Such changes may seem minor but can result in subtle changes of meaning and distractions during the defense.

Dissertation Check List

  • Provide committee members and other attendees a printed copy of your slides.
  • Your presentation is a big deal, dress like it. At the very least dress business casual, but it would not be looked down upon to wear a suit or nice dress.
  • It is customary to provide refreshments for presentation attendees. Depending on the time of day items like bagels, fruit, pastries, sandwiches, or dessert are all fine.
  • Number your slides. This will help your committee members follow along, especially if one of them has to attend remotely.
  • Spell check, spell check, spell check! Science and math are not excuses for poor grammar.
  • Be consistent throughout with references and capitalization. A reminder that Section, Chapter, and Figure are all capitalized.
  • Abbreviations should always be written out upon the first reference.
  • Double check that you are not missing any references.
  • Practice your presentation alone and with colleagues or friends.
  • Arrive well rested and confident. You have worked this hard and now it is time to shine. Your goal is within reach! Good luck!

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